diff --git a/NEWS b/NEWS
index fabf034eb..ff081633a 100644
--- a/NEWS
+++ b/NEWS
@@ -3,6 +3,22 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2021-03-22:
+
+- A new --globcasedetect shell option is added to ksh on OSs where we can check
+  for a case-insensitive file system (currently macOS, Windows/Cygwin, Linux
+  5.2+, and QNX 7.0+). When this option is turned on, file name generation
+  (globbing), as well as file name tab completion on interactive shells,
+  automatically become case-insensitive on file systems where the difference
+  between upper- and lowercase is ignored for file names. This is transparently
+  determined for each directory, so a path pattern that spans multiple file
+  systems can be part case-sensitive and part case-insensitive.
+      The option is not compiled into ksh on systems where we do not know of a
+  method to check for file system case insensitivity. The shell option can be
+  force-compiled by setting SHOPT_GLOBCASEDET to 1 in src/cmd/ksh93/SHOPT.sh,
+  but it won't have any effect on non-supported systems, so this is not
+  recommended. It can be removed from ksh by setting SHOPT_GLOBCASEDET to 0.
+
 2021-03-17:
 
 - Fixed a bug with file name completion on the interactive shell in multibyte
diff --git a/src/cmd/ksh93/SHOPT.sh b/src/cmd/ksh93/SHOPT.sh
index c95f05404..845da9470 100644
--- a/src/cmd/ksh93/SHOPT.sh
+++ b/src/cmd/ksh93/SHOPT.sh
@@ -20,6 +20,7 @@ SHOPT EDPREDICT=1			# predictive editing
 SHOPT ESH=1				# emacs/gmacs edit mode
 SHOPT FILESCAN=1			# fast file scan
 SHOPT FIXEDARRAY=1			# fixed dimension indexed array
+SHOPT GLOBCASEDET=			# -o globcasedetect: adapt globbing/completion to case-insensitive file systems
 SHOPT HISTEXPAND=1			# csh-style history file expansions
 SHOPT KIA=				# ksh -R <outfile> <script> generates cross-ref database from script
 SHOPT MULTIBYTE=1			# multibyte character handling
diff --git a/src/cmd/ksh93/data/options.c b/src/cmd/ksh93/data/options.c
index dae9a7e3c..9ff60fe10 100644
--- a/src/cmd/ksh93/data/options.c
+++ b/src/cmd/ksh93/data/options.c
@@ -43,6 +43,9 @@ const Shtable_t shtab_options[] =
 	"errexit",			SH_ERREXIT,
 	"noexec",			SH_NOEXEC,
 	"noglob",			SH_NOGLOB,
+#if SHOPT_GLOBCASEDET
+	"globcasedetect",		SH_GLOBCASEDET,
+#endif
 	"globstar",			SH_GLOBSTARS,
 #if SHOPT_ESH
 	"gmacs",			SH_GMACS,
diff --git a/src/cmd/ksh93/edit/completion.c b/src/cmd/ksh93/edit/completion.c
index f46e7649a..6ba321589 100644
--- a/src/cmd/ksh93/edit/completion.c
+++ b/src/cmd/ksh93/edit/completion.c
@@ -59,6 +59,9 @@ static char *fmtx(const char *string)
 	return(stakptr(offset));
 }
 
+#if !SHOPT_GLOBCASEDET
+#define charcmp(a,b,dummy) (a==b)
+#else
 static int charcmp(int a, int b, int nocase)
 {
 	if(nocase)
@@ -78,6 +81,7 @@ static int charcmp(int a, int b, int nocase)
 	}
 	return(a==b);
 }
+#endif /* !SHOPT_GLOBCASEDET */
 
 /*
  *  overwrites <str> to common prefix of <str> and <newstr>
@@ -384,8 +388,10 @@ int ed_expand(Edit_t *ep, char outbuff[],int *cur,int *eol,int mode, int count)
 				*dir = 0;
 				saveout = begin;
 			}
-			if(saveout=astconf("PATH_ATTRIBUTES",saveout,(char*)0))
-				nocase = (strchr(saveout,'c')!=0);
+#if SHOPT_GLOBCASEDET
+			if(sh_isoption(SH_GLOBCASEDET))
+				nocase = (pathicase(saveout) > 0);
+#endif
 			if(dir)
 				*dir = c;
 			/* just expand until name is unique */
diff --git a/src/cmd/ksh93/features/options b/src/cmd/ksh93/features/options
index 4150ffcbf..5bd8f73c2 100644
--- a/src/cmd/ksh93/features/options
+++ b/src/cmd/ksh93/features/options
@@ -54,3 +54,18 @@ cat{
 	#   undef SHOPT_MULTIBYTE
 	#endif
 }end
+
+tst	note{ can we probe file system case insensitivity }end output{
+	#include <ast.h>
+	#include <error.h>
+	#include <stdio.h>
+	static char *o = "SHOPT_GLOBCASEDET";
+	int main(int argc,char *argv[])
+	{
+		int r;
+		r = pathicase("/");
+		r = (r > -1 || errno != ENOSYS);
+		printf("#ifndef %s\n#   define %s\t%d\n#endif\n", o, o, r);
+		return !r;
+	}
+}end
diff --git a/src/cmd/ksh93/include/shell.h b/src/cmd/ksh93/include/shell.h
index be9489880..900df6145 100644
--- a/src/cmd/ksh93/include/shell.h
+++ b/src/cmd/ksh93/include/shell.h
@@ -133,6 +133,9 @@ typedef union Shnode_u Shnode_t;
 #define SH_DICTIONARY	30
 #define SH_PIPEFAIL	32
 #define SH_GLOBSTARS	33
+#if SHOPT_GLOBCASEDET
+#define SH_GLOBCASEDET	34
+#endif
 #define SH_RC		35
 #define SH_SHOWME	36
 #define SH_LETOCTAL	37
diff --git a/src/cmd/ksh93/include/version.h b/src/cmd/ksh93/include/version.h
index 6d395d18a..cfd725f34 100644
--- a/src/cmd/ksh93/include/version.h
+++ b/src/cmd/ksh93/include/version.h
@@ -20,7 +20,7 @@
 
 #define SH_RELEASE_FORK	"93u+m"		/* only change if you develop a new ksh93 fork */
 #define SH_RELEASE_SVER	"1.0.0-alpha"	/* semantic version number: https://semver.org */
-#define SH_RELEASE_DATE	"2021-03-17"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2021-03-22"	/* must be in this format for $((.sh.version)) */
 #define SH_RELEASE_CPYR	"(c) 2020-2021 Contributors to ksh " SH_RELEASE_FORK
 
 /* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */
diff --git a/src/cmd/ksh93/sh.1 b/src/cmd/ksh93/sh.1
index e62cc5f52..9c9bf8246 100644
--- a/src/cmd/ksh93/sh.1
+++ b/src/cmd/ksh93/sh.1
@@ -2771,7 +2771,9 @@ currently implemented.
 The remainder of the pattern uses System V regular expression syntax.
 .TP
 .B i
-Treat the match as case insensitive.
+Always treat the match as case-insensitive, regardless of the
+.B globcasedetect
+shell option.
 .TP
 .B g
 File the longest match (greedy).  This is the default.
@@ -6008,7 +6010,7 @@ omitted, then \f2type\^\fP must be an indexed array variable with at
 least two elements and the values are taken from this array variable.
 If
 .B -i
-is specified the values are case insensitive.
+is specified the values are case-insensitive.
 Declaration commands are created as special builtins that cannot be
 removed or overridden by shell functions.
 .TP
@@ -7122,6 +7124,22 @@ style in-line editor for command entry.
 Same as
 .BR \-e .
 .TP 8
+.B globcasedetect
+When this option is turned on, globbing (see
+.I "File Name Generation\^"
+above) and
+file name listing and completion (see
+.I "In-line Editing Options\^"
+above) automatically become case-insensitive on file systems where the
+difference between upper- and lowercase is ignored for file names. This is
+transparently determined for each directory, so a path pattern that spans
+multiple file systems can be part case-sensitive and part case-insensitive.
+In more precise terms, each slash-separated path name component pattern \fIp\fR
+is treated as \fB~(i:\fR\fIp\fR\fB)\fR
+if its parent directory exists on a case-insensitive file system.
+This option is only present on operating systems that support
+case-insensitive file systems.
+.TP 8
 .B globstar
 Same as
 .BR \-G .
diff --git a/src/cmd/ksh93/sh/expand.c b/src/cmd/ksh93/sh/expand.c
index 39f81e0dc..9acb9fbe3 100644
--- a/src/cmd/ksh93/sh/expand.c
+++ b/src/cmd/ksh93/sh/expand.c
@@ -92,6 +92,10 @@ int path_expand(Shell_t *shp,const char *pattern, struct argnod **arghead)
 		flags |= GLOB_MARK;
 	if(sh_isoption(SH_GLOBSTARS))
 		flags |= GLOB_STARSTAR;
+#if SHOPT_GLOBCASEDET
+	if(sh_isoption(SH_GLOBCASEDET))
+		flags |= GLOB_DCASE;
+#endif
 	if(sh_isstate(SH_COMPLETE))
 	{
 #if KSHELL
diff --git a/src/lib/libast/Mamfile b/src/lib/libast/Mamfile
index 8b4a111d5..86e462ae4 100644
--- a/src/lib/libast/Mamfile
+++ b/src/lib/libast/Mamfile
@@ -1028,6 +1028,15 @@ make install
 				prev path/pathfind.c
 				exec - ${CC} ${mam_cc_FLAGS} ${KSH_RELFLAGS} ${CCFLAGS} -I. -Icomp -Iinclude -Istd -D_PACKAGE_ast -c path/pathfind.c
 			done pathfind.o generated
+			make pathicase.o
+				make path/pathicase.c
+					prev include/error.h implicit
+					prev include/ast.h implicit
+				done path/pathicase.c
+				meta pathicase.o %.c>%.o path/pathicase.c pathicase
+				prev path/pathicase.c
+				exec - ${CC} ${mam_cc_FLAGS} ${KSH_RELFLAGS} ${CCFLAGS} -I. -Icomp -Iinclude -Istd -D_PACKAGE_ast -c path/pathicase.c
+			done pathicase.o generated
 			make pathkey.o
 				make path/pathkey.c
 					prev ast_api.h implicit
@@ -6081,7 +6090,7 @@ make install
 				exec - ${CC} ${mam_cc_FLAGS} ${KSH_RELFLAGS} ${CCFLAGS} -I. -Icomp -Iinclude -Istd -D__OBSOLETE__=20120101 -D_PACKAGE_ast -c disc/sfstrtmp.c
 			done sfstrtmp.o generated
 			exec - ${AR} rc libast.a state.o transition.o opendir.o readdir.o rewinddir.o seekdir.o telldir.o getcwd.o fastfind.o hashalloc.o hashdump.o hashfree.o hashlast.o hashlook.o hashscan.o hashsize.o hashview.o hashwalk.o memhash.o memsum.o strhash.o strkey.o strsum.o stracmp.o strnacmp.o ccmap.o ccmapid.o ccnative.o chresc.o chrtoi.o
-			exec - ${AR} rc libast.a streval.o strexpr.o strmatch.o strcopy.o modei.o modex.o strmode.o strlcat.o strlcpy.o strlook.o strncopy.o strsearch.o strpsearch.o stresc.o stropt.o strtape.o strpcmp.o strnpcmp.o strvcmp.o strnvcmp.o tok.o tokline.o tokscan.o pathaccess.o pathcat.o pathcanon.o pathcheck.o pathpath.o pathexists.o pathfind.o pathkey.o pathprobe.o pathrepl.o pathnative.o pathposix.o pathtemp.o pathtmp.o pathstat.o pathgetlink.o pathsetlink.o pathbin.o pathshell.o pathcd.o pathprog.o ftwalk.o ftwflags.o fts.o astintercept.o conformance.o getenv.o setenviron.o optget.o optjoin.o optesc.o optctx.o strsort.o struniq.o magic.o mime.o mimetype.o signal.o sigflag.o systrace.o error.o errorf.o errormsg.o errorx.o localeconv.o setlocale.o translate.o catopen.o iconv.o lc.o lctab.o mc.o base64.o recfmt.o recstr.o reclen.o fmtrec.o fmtbase.o fmtbuf.o fmtclock.o fmtdev.o fmtelapsed.o fmterror.o fmtesc.o fmtfmt.o fmtfs.o fmtident.o fmtint.o fmtip4.o fmtip6.o fmtls.o fmtmatch.o fmtmode.o fmtnum.o fmtperm.o fmtre.o fmttime.o
+			exec - ${AR} rc libast.a streval.o strexpr.o strmatch.o strcopy.o modei.o modex.o strmode.o strlcat.o strlcpy.o strlook.o strncopy.o strsearch.o strpsearch.o stresc.o stropt.o strtape.o strpcmp.o strnpcmp.o strvcmp.o strnvcmp.o tok.o tokline.o tokscan.o pathaccess.o pathcat.o pathcanon.o pathcheck.o pathpath.o pathexists.o pathfind.o pathicase.o pathkey.o pathprobe.o pathrepl.o pathnative.o pathposix.o pathtemp.o pathtmp.o pathstat.o pathgetlink.o pathsetlink.o pathbin.o pathshell.o pathcd.o pathprog.o ftwalk.o ftwflags.o fts.o astintercept.o conformance.o getenv.o setenviron.o optget.o optjoin.o optesc.o optctx.o strsort.o struniq.o magic.o mime.o mimetype.o signal.o sigflag.o systrace.o error.o errorf.o errormsg.o errorx.o localeconv.o setlocale.o translate.o catopen.o iconv.o lc.o lctab.o mc.o base64.o recfmt.o recstr.o reclen.o fmtrec.o fmtbase.o fmtbuf.o fmtclock.o fmtdev.o fmtelapsed.o fmterror.o fmtesc.o fmtfmt.o fmtfs.o fmtident.o fmtint.o fmtip4.o fmtip6.o fmtls.o fmtmatch.o fmtmode.o fmtnum.o fmtperm.o fmtre.o fmttime.o
 			exec - ${AR} rc libast.a fmtuid.o fmtgid.o fmtsignal.o fmtscale.o fmttmx.o fmttv.o fmtversion.o strelapsed.o strperm.o struid.o strgid.o strtoip4.o strtoip6.o stack.o stk.o swapget.o swapmem.o swapop.o swapput.o sigdata.o sigcrit.o sigunblock.o procopen.o procclose.o procrun.o procfree.o tmdate.o tmequiv.o tmfix.o tmfmt.o tmform.o tmgoff.o tminit.o tmleap.o tmlex.o tmlocale.o tmmake.o tmpoff.o tmscan.o tmsleep.o tmtime.o tmtype.o tmweek.o tmword.o tmzone.o tmxdate.o tmxduration.o tmxfmt.o tmxgettime.o tmxleap.o tmxmake.o tmxscan.o tmxsettime.o tmxsleep.o tmxtime.o tmxtouch.o tvcmp.o tvgettime.o tvsettime.o tvsleep.o tvtouch.o cmdarg.o vecargs.o vecfile.o vecfree.o vecload.o vecstring.o univdata.o touch.o mnt.o debug.o memccpy.o memchr.o memcmp.o memcpy.o memdup.o memmove.o memset.o mkdir.o mkfifo.o mknod.o rmdir.o remove.o rename.o link.o unlink.o strdup.o strchr.o strrchr.o strstr.o strtod.o strtold.o strtol.o strtoll.o strtoul.o strtoull.o strton.o strtonll.o strntod.o strntold.o strnton.o
 			exec - ${AR} rc libast.a strntonll.o strntol.o strntoll.o strntoul.o strntoull.o strcasecmp.o strncasecmp.o strerror.o mktemp.o tmpnam.o fsync.o execlp.o execve.o execvp.o execvpe.o spawnveg.o vfork.o killpg.o hsearch.o tsearch.o getlogin.o putenv.o setenv.o unsetenv.o lstat.o statvfs.o eaccess.o gross.o omitted.o readlink.o symlink.o getpgrp.o setpgid.o setsid.o waitpid.o creat64.o fcntl.o open.o atexit.o getdents.o getwd.o dup2.o errno.o getpreroot.o ispreroot.o realopen.o setpreroot.o getgroups.o mount.o system.o iblocks.o modedata.o tmdata.o memfatal.o sfkeyprintf.o sfdcdio.o sfdcdos.o sfdcfilter.o sfdcseekable.o sfdcslow.o sfdcsubstr.o sfdctee.o sfdcunion.o sfdcmore.o sfdcprefix.o wc.o wc2utf8.o basename.o closelog.o dirname.o fmtmsglib.o fnmatch.o ftw.o getdate.o getsubopt.o glob.o nftw.o openlog.o re_comp.o resolvepath.o realpath.o regcmp.o regexp.o setlogmask.o strftime.o strptime.o swab.o syslog.o tempnam.o wordexp.o mktime.o regalloc.o regclass.o regcoll.o regcomp.o regcache.o regdecomp.o regerror.o regexec.o regfatal.o reginit.o
 			exec - ${AR} rc libast.a regnexec.o regsubcomp.o regsubexec.o regsub.o regrecord.o regrexec.o regstat.o dtclose.o dtdisc.o dthash.o dtlist.o dtmethod.o dtopen.o dtstat.o dtstrhash.o dttree.o dtuser.o dtview.o dtwalk.o dtnew.o dtcomp.o sfclose.o sfclrlock.o sfdisc.o sfdlen.o sfexcept.o sfgetl.o sfgetu.o sfcvt.o sfecvt.o sffcvt.o sfextern.o sffilbuf.o sfflsbuf.o sfprints.o sfgetd.o sfgetr.o sfllen.o sfmode.o sfmove.o sfnew.o sfpkrd.o sfnotify.o sfnputc.o sfopen.o sfpeek.o sfpoll.o sfpool.o sfpopen.o sfprintf.o sfputd.o sfputl.o sfputr.o sfputu.o sfrd.o sfread.o sfreserve.o sfscanf.o sfseek.o sfset.o sfsetbuf.o sfsetfd.o sfsize.o sfsk.o sfstack.o sfstrtod.o sfsync.o sfswap.o sftable.o sftell.o sftmp.o sfungetc.o sfvprintf.o sfvscanf.o sfwr.o sfwrite.o sfpurge.o sfraise.o sfwalk.o sfgetm.o sfmutex.o sfputm.o sfresize.o _sfclrerr.o _sfeof.o _sferror.o _sffileno.o _sfopen.o _sfstacked.o _sfvalue.o _sfgetc.o _sfgetl.o _sfgetl2.o _sfgetu.o _sfgetu2.o _sfdlen.o _sfllen.o _sfslen.o _sfulen.o _sfputc.o _sfputd.o _sfputl.o _sfputm.o
diff --git a/src/lib/libast/features/lib b/src/lib/libast/features/lib
index 5a9a67b2c..4289f78d2 100644
--- a/src/lib/libast/features/lib
+++ b/src/lib/libast/features/lib
@@ -4,6 +4,7 @@ cmd	universe
 
 hdr	dirent,direntry,filio,fmtmsg,fnmatch,jioctl,libgen,limits
 hdr	locale,ndir,nl_types,process,spawn,syslog,utime,vfork
+hdr	linux/fs,sys/ioctl
 hdr	wchar note{ <wchar.h> and isw*() really work }end execute{
 	#include <wchar.h>
 	int
diff --git a/src/lib/libast/include/ast.h b/src/lib/libast/include/ast.h
index 308d8f680..c4ca23b0c 100644
--- a/src/lib/libast/include/ast.h
+++ b/src/lib/libast/include/ast.h
@@ -317,6 +317,7 @@ extern int		pathcheck(const char*, const char*, Pathcheck_t*);
 extern int		pathexists(char*, int);
 extern char*		pathfind(const char*, const char*, const char*, char*, size_t);
 extern int		pathgetlink(const char*, char*, int);
+extern int		pathicase(const char*);
 extern int		pathinclude(const char*);
 extern char*		pathkey(char*, char*, const char*, const char*, const char*);
 extern char*		pathkey_20100601(const char*, const char*, const char*, char*, size_t, char*, size_t);
diff --git a/src/lib/libast/include/glob.h b/src/lib/libast/include/glob.h
index d1b5b1526..911d6ae19 100644
--- a/src/lib/libast/include/glob.h
+++ b/src/lib/libast/include/glob.h
@@ -94,6 +94,11 @@ struct _glob_
 
 };
 
+/*
+ * The standard/extended interface GLOB_* flags below must
+ * fit in the GLOB_FLAGMASK bitmask defined in misc/glob.c.
+ */
+
 /* standard interface */
 #define GLOB_APPEND	0x0001		/* append to previous		*/
 #define GLOB_DOOFFS	0x0002		/* gl_offs defines argv offset	*/
@@ -113,8 +118,8 @@ struct _glob_
 #define GLOB_LIST	0x2000		/* just create gl_list		*/
 #define GLOB_ALTDIRFUNC	0x4000		/* gnu discipline functions	*/
 #define GLOB_DISC	0x8000		/* discipline initialized	*/
-
 #define GLOB_GROUP	0x10000		/* REG_SHELL_GROUP		*/
+#define GLOB_DCASE	0x20000		/* detect FS case insensitivity	*/
 
 /* gl_status */
 #define GLOB_NOTDIR	0x0001		/* last gl_dirnext() not a dir	*/
diff --git a/src/lib/libast/man/path.3 b/src/lib/libast/man/path.3
index 3e72714e7..3b0d4be05 100644
--- a/src/lib/libast/man/path.3
+++ b/src/lib/libast/man/path.3
@@ -50,6 +50,7 @@ char*     pathcat(char* \fIpath\fP, const char* \fIdirs\fP, int \fIsep\fP, const
 char*     pathcd(char* \fIpath\fP, const char* \fIhome\fP);
 int       pathcheck(const char* \fIpackage\fP, const char* \fItool\fP, Pathcheck_t* \fIpc\fP);
 int       pathgetlink(const char* \fIname\fP, char* \fIbuf\fP, int \fIsiz\fP);
+int       pathicase(const char* \fIpath\fP);
 char*     pathkey(char* \fIkey\fP, char* \fIattr\fP, const char* \fIlang\fP, const char* \fIpath\fP);
 char*     pathnext(char* \fIpath\fP, char* \fIextra\fP, long* \fIvisits\fP);
 char*     pathpath(char* \fIpath\fP, const char* \fIp\fP, const char* \fIa\fP, int \fImode\fP);
@@ -230,6 +231,32 @@ by converting non-standard dynamic link text to
 .L pathsetsymlink
 converts in the other direction.
 .PP
+.L pathicase
+uses an operating system-specific method, if available,
+to determine if a file system uses case-insensitive file names.
+The return value is
+.B 1
+if the file system associated with the
+.I path
+is case-insensitive (regardless of case preservation),
+.B 0
+if it is not, or
+.B \-1
+if an error occurred. On error,
+.L errno
+is set by the system-specific function that was used.
+If the operating system does not have a known method
+to determine file system case insensitivity for the
+.IR path ,
+then
+.L pathicase
+returns
+.B \-1
+with
+.L errno
+set to
+.LR ENOSYS .
+.PP
 .L pathkey
 generates in
 .I key
diff --git a/src/lib/libast/misc/glob.c b/src/lib/libast/misc/glob.c
index 267283b2d..3990b4786 100644
--- a/src/lib/libast/misc/glob.c
+++ b/src/lib/libast/misc/glob.c
@@ -37,7 +37,12 @@
 #include <ctype.h>
 #include <regex.h>
 
-#define GLOB_MAGIC	0xaaaa0000
+/*
+ * GLOB_MAGIC is used for sanity checking. Its significant bits must not overlap with those used
+ * for flags. If a new GLOB_* flag bit is added to glob.h, these must be adapted accordingly.
+ */
+#define GLOB_MAGIC	0xAAA80000	/* 10101010101010000000000000000000 */
+#define GLOB_FLAGMASK	0x0003FFFF	/* 00000000000000111111111111111111 */
 
 #define MATCH_RAW	1
 #define MATCH_MAKE	2
@@ -143,7 +148,9 @@ gl_type(glob_t* gp, const char* path, int flags)
 static int
 gl_attr(glob_t* gp, const char* path, int flags)
 {
-	return strchr(astconf("PATH_ATTRIBUTES", path, NiL), 'c') ? GLOB_ICASE : 0;
+	NOT_USED(gp);
+	NOT_USED(flags);
+	return pathicase(path) > 0 ? GLOB_ICASE : 0;
 }
 
 /*
@@ -485,7 +492,9 @@ skip:
 			|| t1 == GLOB_SYM && pat[0]=='*' && pat[1]=='\0') /* follow symlinks to dirs for non-globstar components */
 		&& (dirf = (*gp->gl_diropen)(gp, dirname)))
 		{
-			if (!(gp->re_flags & REG_ICASE) && ((*gp->gl_attr)(gp, dirname, 0) & GLOB_ICASE))
+			if (!(gp->re_flags & REG_ICASE)
+			&& (gp->gl_flags & GLOB_DCASE)
+			&& ((*gp->gl_attr)(gp, dirname, 0) & GLOB_ICASE))
 			{
 				if (!prei)
 				{
@@ -613,7 +622,7 @@ glob(const char* pattern, int flags, int (*errfn)(const char*, int), register gl
 	}
 	else
 	{
-		gp->gl_flags = (flags&0xffff)|GLOB_MAGIC;
+		gp->gl_flags = (flags & GLOB_FLAGMASK) | GLOB_MAGIC;
 		gp->re_flags = REG_SHELL|REG_NOSUB|REG_LEFT|REG_RIGHT|((flags&GLOB_AUGMENTED)?REG_AUGMENTED:0);
 		gp->gl_pathc = 0;
 		gp->gl_ignore = 0;
@@ -730,7 +739,7 @@ glob(const char* pattern, int flags, int (*errfn)(const char*, int), register gl
 					f &= ~GLOB_STARSTAR;
 				continue;
 			case ')':
-				flags = (gp->gl_flags = f) & 0xffff;
+				flags = (gp->gl_flags = f) & GLOB_FLAGMASK;
 				if (f & GLOB_ICASE)
 					gp->re_flags |= REG_ICASE;
 				else
diff --git a/src/lib/libast/path/pathexists.c b/src/lib/libast/path/pathexists.c
index c0c5277af..98572304e 100644
--- a/src/lib/libast/path/pathexists.c
+++ b/src/lib/libast/path/pathexists.c
@@ -63,7 +63,7 @@ pathexists(char* path, int mode)
 
 	t = &tree;
 	e = (c = *path) == '/' ? path + 1 : path;
-	cmp = strchr(astconf("PATH_ATTRIBUTES", path, NiL), 'c') ? strcasecmp : strcmp;
+	cmp = pathicase(path) > 0 ? strcasecmp : strcmp;
 	if ((ast.locale.set & (AST_LC_debug|AST_LC_find)) == (AST_LC_debug|AST_LC_find))
 		sfprintf(sfstderr, "locale test %s\n", path);
 	while (c)
diff --git a/src/lib/libast/path/pathicase.c b/src/lib/libast/path/pathicase.c
new file mode 100644
index 000000000..8418b2e29
--- /dev/null
+++ b/src/lib/libast/path/pathicase.c
@@ -0,0 +1,59 @@
+/***********************************************************************
+*                                                                      *
+*              This file is part of the ksh 93u+m package              *
+*             Copyright (c) 2021 Contributors to ksh 93u+m             *
+*                    <https://github.com/ksh93/ksh>                    *
+*                      and is licensed under the                       *
+*                 Eclipse Public License, Version 1.0                  *
+*                                                                      *
+*                A copy of the License is available at                 *
+*          http://www.eclipse.org/org/documents/epl-v10.html           *
+*         (with md5 checksum b35adb5213ca9657e911e9befb180842)         *
+*                                                                      *
+*                  Martijn Dekker <martijn@inlv.org>                   *
+*                                                                      *
+***********************************************************************/
+
+#include <ast.h>
+#include <error.h>
+
+#if _hdr_linux_fs && _hdr_sys_ioctl
+#include <linux/fs.h>
+#include <sys/ioctl.h>
+#endif
+
+/*
+ * Return 1 if the given path is on a case insensitive file system, 0 if not, -1 on error.
+ */
+int
+pathicase(const char *path)
+{
+#ifdef _PC_PATH_ATTRIBUTES
+	/* AT&T mystery system (AST UWIN?) */
+	char *a = astconf("PATH_ATTRIBUTES", path, (char*)0);
+	return a ? strchr(a,'c') != 0 : -1;
+#elif _lib_pathconf && defined(_PC_CASE_SENSITIVE)
+	/* macOS; QNX 7.0+ */
+	long r = pathconf(path, _PC_CASE_SENSITIVE);
+	return r < 0L ? -1 : r == 0L;
+#elif _lib_pathconf && defined(_PC_CASE_INSENSITIVE)
+	/* Cygwin */
+	long r = pathconf(path, _PC_CASE_INSENSITIVE);
+	return r < 0L ? -1 : r > 0L;
+#elif _hdr_linux_fs && _hdr_sys_ioctl && defined(FS_IOC_GETFLAGS) && defined(FS_CASEFOLD_FL)
+	/* Linux 5.2+ */
+	int attr = 0, fd, r;
+	if ((fd = open(path, O_RDONLY|O_NONBLOCK)) < 0)
+		return -1;
+	r = ioctl(fd, FS_IOC_GETFLAGS, &attr);
+	close(fd);
+	return r < 0 ? -1 : attr & FS_CASEFOLD_FL != 0;
+#elif _WINIX || __APPLE__
+	/* Windows or Mac without pathconf probe: assume case insensitive */
+	return 1;
+#else
+	/* Not implemented */
+	errno = ENOSYS;
+	return -1;
+#endif
+}
diff --git a/src/lib/libast/port/astconf.c b/src/lib/libast/port/astconf.c
index 4d9b83aac..b69b77546 100644
--- a/src/lib/libast/port/astconf.c
+++ b/src/lib/libast/port/astconf.c
@@ -221,11 +221,7 @@ static Feature_t	dynamic[] =
 	{
 		&dynamic[OP_path_attributes+1],
 		"PATH_ATTRIBUTES",
-#if _WINIX
-		"c",
-#else
 		&null[0],
-#endif
 		&null[0],
 		0,
 		15,
@@ -706,6 +702,8 @@ format(register Feature_t* fp, const char* path, const char* value, unsigned int
 				}
 			*s = 0;
 		}
+#else
+		fp->value = pathicase(path) > 0 ? "c" : null;
 #endif
 		break;