diff --git a/Makefile b/Makefile
index 6b62c2e645..b202b95c02 100644
--- a/Makefile
+++ b/Makefile
@@ -79,7 +79,7 @@ endif
 
 # Check code syntax with host compiler
 CHECK_WARNINGS := -Wall -Wextra -Wno-format-security -Wno-unknown-pragmas -Wno-unused-parameter -Wno-unused-variable -Wno-missing-braces -Wno-int-conversion -Wno-unused-but-set-variable -Wno-unused-label
-CC_CHECK   := gcc -fno-builtin -fsyntax-only -funsigned-char -fdiagnostics-color -std=gnu90 -D _LANGUAGE_C -D NON_MATCHING $(IINC) -include stdarg.h $(CHECK_WARNINGS)
+CC_CHECK   := gcc -fno-builtin -fsyntax-only -funsigned-char -fdiagnostics-color -std=gnu89 -D _LANGUAGE_C -D NON_MATCHING $(IINC) -nostdinc $(CHECK_WARNINGS)
 
 CPP        := cpp
 ELF2ROM    := tools/buildtools/elf2rom
@@ -92,7 +92,7 @@ ASFLAGS := -march=vr4300 -32 -Iinclude
 MIPS_VERSION := -mips2
 
 # we support Microsoft extensions such as anonymous structs, which the compiler does support but warns for their usage. Surpress the warnings with -woff.
-CFLAGS += -G 0 -non_shared -Xfullwarn -Xcpluscomm $(IINC) -Wab,-r4300_mul -woff 624,649,838,712
+CFLAGS += -G 0 -non_shared -Xfullwarn -Xcpluscomm $(IINC) -nostdinc -Wab,-r4300_mul -woff 624,649,838,712
 
 ifeq ($(shell getconf LONG_BIT), 32)
   # Work around memory allocation bug in QEMU
diff --git a/include/assert.h b/include/assert.h
deleted file mode 100644
index 04831e48f1..0000000000
--- a/include/assert.h
+++ /dev/null
@@ -1,4 +0,0 @@
-#ifndef _ASSERT_H_
-#define _ASSERT_H_
-
-#endif
diff --git a/include/convert.h b/include/convert.h
index 456e4b1982..c453e18e3a 100644
--- a/include/convert.h
+++ b/include/convert.h
@@ -1,7 +1,7 @@
 #ifndef _ULTRA64_CONVERT_H_
 #define _ULTRA64_CONVERT_H_
 
-#include "stdint.h"
+#include "libc/stdint.h"
 
 #define OS_CLOCK_RATE           62500000LL
 #define OS_CPU_COUNTER          (OS_CLOCK_RATE*3/4)
diff --git a/include/functions.h b/include/functions.h
index 1cacc5fed2..ad01b7a82c 100644
--- a/include/functions.h
+++ b/include/functions.h
@@ -3,13 +3,6 @@
 
 #include "z64.h"
 
-float fabsf(float f);
-#pragma intrinsic(fabsf)
-float sqrtf(float f);
-#pragma intrinsic(sqrtf)
-double sqrt(double d);
-#pragma intrinsic(sqrt)
-
 void bootproc(void);
 void Idle_ThreadEntry(void* arg);
 void ViConfig_UpdateVi(u32 arg0);
diff --git a/include/ichain.h b/include/ichain.h
index 8b11121911..f9131545c2 100644
--- a/include/ichain.h
+++ b/include/ichain.h
@@ -1,6 +1,8 @@
 #ifndef _ICHAIN_H_
 #define _ICHAIN_H_
 
+#include "libc/stddef.h"
+
 typedef struct {
     u32 cont:   1;
     u32 type:   4;
@@ -8,8 +10,6 @@ typedef struct {
     s32 value:  16;
 } InitChainEntry;
 
-#define OFFSETOF(structure, member) ((size_t)&(((structure*)0)->member))
-
 typedef enum {
     /* 0x0 */ ICHAINTYPE_U8,            // sets byte
     /* 0x1 */ ICHAINTYPE_S8,
@@ -38,7 +38,7 @@ typedef enum {
  * * cont ----- ICHAIN_CONTINUE (or ICHAIN_STOP) to continue (or stop) parsing
  */
 #define ICHAIN(type, member, value, cont)      \
-        { cont, type, OFFSETOF(Actor, member), value }
+        { cont, type, offsetof(Actor, member), value }
 
 #define ICHAIN_U8(member, val, cont)            ICHAIN(ICHAINTYPE_U8, member, val, cont)
 #define ICHAIN_S8(member, val, cont)            ICHAIN(ICHAINTYPE_S8, member, val, cont)
diff --git a/include/alloca.h b/include/libc/alloca.h
similarity index 100%
rename from include/alloca.h
rename to include/libc/alloca.h
diff --git a/include/libc/assert.h b/include/libc/assert.h
new file mode 100644
index 0000000000..1bc72e3144
--- /dev/null
+++ b/include/libc/assert.h
@@ -0,0 +1,4 @@
+#ifndef ASSERT_H
+#define ASSERT_H
+
+#endif
diff --git a/include/math.h b/include/libc/math.h
similarity index 74%
rename from include/math.h
rename to include/libc/math.h
index 20fa352faa..c6756d959f 100644
--- a/include/math.h
+++ b/include/libc/math.h
@@ -1,5 +1,5 @@
-#ifndef _MATH_H_
-#define _MATH_H_
+#ifndef MATH_H
+#define MATH_H
 
 #include "PR/ultratypes.h"
 
@@ -26,4 +26,11 @@ typedef union {
 
 extern f32 __libm_qnan_f;
 
+float fabsf(float f);
+#pragma intrinsic(fabsf)
+float sqrtf(float f);
+#pragma intrinsic(sqrtf)
+double sqrt(double d);
+#pragma intrinsic(sqrt)
+
 #endif
diff --git a/include/stdarg.h b/include/libc/stdarg.h
similarity index 96%
rename from include/stdarg.h
rename to include/libc/stdarg.h
index 26a67e5801..77b8b8866c 100644
--- a/include/stdarg.h
+++ b/include/libc/stdarg.h
@@ -1,5 +1,5 @@
-#ifndef _STDARG_H_
-#define _STDARG_H_
+#ifndef STDARG_H
+#define STDARG_H
 
 #include "ultra64.h"
 
@@ -41,5 +41,6 @@ typedef char *va_list;
                                           : __va_stack_arg(list, mode))))[-1]
 #define va_end(__list)
 
-#endif
-#endif
+#endif /* __GNUC__ */
+
+#endif /* STDARG_H */
diff --git a/include/stdbool.h b/include/libc/stdbool.h
similarity index 72%
rename from include/stdbool.h
rename to include/libc/stdbool.h
index 519806b310..d441054c1d 100644
--- a/include/stdbool.h
+++ b/include/libc/stdbool.h
@@ -1,5 +1,5 @@
-#ifndef _STDBOOL
-#define _STDBOOL
+#ifndef STDBOOL
+#define STDBOOL
 
 #define __bool_true_false_are_defined 1
 
@@ -11,4 +11,4 @@
 
 #endif /* __cplusplus */
 
-#endif /* _STDBOOL */
+#endif /* STDBOOL */
diff --git a/include/libc/stddef.h b/include/libc/stddef.h
new file mode 100644
index 0000000000..4f55e5725e
--- /dev/null
+++ b/include/libc/stddef.h
@@ -0,0 +1,20 @@
+#ifndef STDDEF_H
+#define STDDEF_H
+
+#include "PR/ultratypes.h"
+
+typedef u32 size_t;
+
+typedef s32 ptrdiff_t;
+
+#ifndef NULL
+#define NULL (void*)0
+#endif
+
+#ifdef __GNUC__
+#define offsetof(structure, member) __builtin_offsetof (structure, member)
+#else
+#define offsetof(structure, member) ((size_t)&(((structure*)0)->member))
+#endif
+
+#endif /* STDDEF_H */
diff --git a/include/stdint.h b/include/libc/stdint.h
similarity index 86%
rename from include/stdint.h
rename to include/libc/stdint.h
index 67e9e68622..1696615a7c 100644
--- a/include/stdint.h
+++ b/include/libc/stdint.h
@@ -1,7 +1,7 @@
-#ifndef _STDINT_H_
-#define _STDINT_H_
+#ifndef STDINT_H
+#define STDINT_H
 
-#include "ultra64.h"
+#include "PR/ultratypes.h"
 
 typedef s32 intptr_t;
 typedef u32 uintptr_t;
@@ -26,4 +26,4 @@ typedef u32 uintptr_t;
 #define UINTPTR_MAX 0xffffffff
 
 
-#endif /* _STDINT_H_ */
+#endif /* STDINT_H */
diff --git a/include/stdlib.h b/include/libc/stdlib.h
similarity index 77%
rename from include/stdlib.h
rename to include/libc/stdlib.h
index a7b44961a9..57d352a13c 100644
--- a/include/stdlib.h
+++ b/include/libc/stdlib.h
@@ -1,27 +1,25 @@
-#ifndef _STDLIB_H_
-#define _STDLIB_H_
+#ifndef STDLIB_H
+#define STDLIB_H
+
+#include "libc/stddef.h"
 
 typedef struct {
     /* 0x0 */ int quot;
     /* 0x4 */ int rem;
 } div_t;
 
-
 typedef struct {
     /* 0x0 */ long quot;
     /* 0x4 */ long rem;
 } ldiv_t;
 
-
 typedef struct {
     /* 0x0 */ long long quot;
     /* 0x8 */ long long rem;
 } lldiv_t;
 
-typedef unsigned long size_t;
-
 typedef int ssize_t;
 
 typedef long wchar_t;
 
-#endif
+#endif /* STDLIB_H */
diff --git a/include/macros.h b/include/macros.h
index 7dd84fc8ee..2cff3c814d 100644
--- a/include/macros.h
+++ b/include/macros.h
@@ -1,7 +1,7 @@
 #ifndef _MACROS_H_
 #define _MACROS_H_
 
-#include "stdint.h"
+#include "libc/stdint.h"
 #include "convert.h"
 #include "z64.h"
 
diff --git a/include/os.h b/include/os.h
index f892398748..e9a5da37dc 100644
--- a/include/os.h
+++ b/include/os.h
@@ -1,7 +1,7 @@
 #ifndef _OS_H_
 #define _OS_H_
 
-#include "stdlib.h"
+#include "libc/stdlib.h"
 #include "ultra64/thread.h"
 #include "ultra64/message.h"
 
diff --git a/include/osint.h b/include/osint.h
index f4da044c60..71781ab6da 100644
--- a/include/osint.h
+++ b/include/osint.h
@@ -3,7 +3,7 @@
 
 // TODO should be in libultra/os
 
-#include "stdarg.h"
+#include "libc/stdarg.h"
 #include "os.h"
 #include "os_internal.h"
 #include "ultraerror.h"
diff --git a/include/xstdio.h b/include/xstdio.h
index bb297e5900..102a25ee4c 100644
--- a/include/xstdio.h
+++ b/include/xstdio.h
@@ -1,6 +1,7 @@
 #ifndef _XSTDIO_H_
 #define _XSTDIO_H_
-#include "stdarg.h"
+
+#include "libc/stdarg.h"
 
 typedef struct {
     /* 0x0 */ union {
diff --git a/include/z64.h b/include/z64.h
index 6def660e08..99f05d653e 100644
--- a/include/z64.h
+++ b/include/z64.h
@@ -1,16 +1,17 @@
 #ifndef _Z64_H_
 #define _Z64_H_
 
-#include "stdarg.h"
-#include "stdbool.h"
-#include "stdint.h"
+#include "libc/math.h"
+#include "libc/stdarg.h"
+#include "libc/stdbool.h"
+#include "libc/stddef.h"
+#include "libc/stdint.h"
+#include "libc/stdlib.h"
 
 #include "ultra64.h"
 #include "io/controller.h"
 #include "osint.h"
-#include "math.h"
 #include "os.h"
-#include "stdlib.h"
 #include "xstdio.h"
 
 #include "bgm.h"
diff --git a/src/libultra/gu/cosf.c b/src/libultra/gu/cosf.c
index 72d154d700..b71ba72341 100644
--- a/src/libultra/gu/cosf.c
+++ b/src/libultra/gu/cosf.c
@@ -1,4 +1,4 @@
-#include "math.h"
+#include "libc/math.h"
 #include "macros.h"
 
 // A slightly tweaked form of the coefficients of the Maclaurin series of sine up to x^9
diff --git a/src/libultra/gu/sinf.c b/src/libultra/gu/sinf.c
index 5f3455ec54..746d141a4a 100644
--- a/src/libultra/gu/sinf.c
+++ b/src/libultra/gu/sinf.c
@@ -1,4 +1,4 @@
-#include "math.h"
+#include "libc/math.h"
 #include "macros.h"
 
 // A slightly tweaked form of the coefficients of the Maclaurin series of sine up to x^9
diff --git a/src/libultra/gu/sins.c b/src/libultra/gu/sins.c
index 69b3b7e391..39bc7ce0c1 100644
--- a/src/libultra/gu/sins.c
+++ b/src/libultra/gu/sins.c
@@ -1,4 +1,4 @@
-#include "math.h"
+#include "libc/math.h"
 
 static s16 sintable[0x400] = {
     0x0000, 0x0032, 0x0064, 0x0096, 0x00C9, 0x00FB, 0x012D, 0x0160, 0x0192, 0x01C4, 0x01F7, 0x0229, 0x025B, 0x028E,
diff --git a/src/libultra/os/virtualtophysical.c b/src/libultra/os/virtualtophysical.c
index 40d2864798..6bdb2ccb3d 100644
--- a/src/libultra/os/virtualtophysical.c
+++ b/src/libultra/os/virtualtophysical.c
@@ -1,6 +1,6 @@
 #include "PR/ultratypes.h"
 #include "osint.h"
-#include "stdint.h"
+#include "libc/stdint.h"
 #include "global.h"
 
 uintptr_t osVirtualToPhysical(void* virtualAddress) {
diff --git a/src/overlays/gamestates/ovl_select/z_select.c b/src/overlays/gamestates/ovl_select/z_select.c
index d58f7ac856..550bbbc8e0 100644
--- a/src/overlays/gamestates/ovl_select/z_select.c
+++ b/src/overlays/gamestates/ovl_select/z_select.c
@@ -5,7 +5,7 @@
  */
 
 #include "z_select.h"
-#include "alloca.h"
+#include "libc/alloca.h"
 #include "overlays/gamestates/ovl_title/z_title.h"
 
 void Select_LoadTitle(SelectContext* this) {