diff --git a/float.h b/float.h
index e74fb7b..e0cecf6 100644
--- a/float.h
+++ b/float.h
@@ -12,8 +12,8 @@
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-#ifndef __FSTD_HDRS_FLOAT_H
-#define __FSTD_HDRS_FLOAT_H 1
+#ifndef __FREESTND_C_HDRS_FLOAT_H
+#define __FREESTND_C_HDRS_FLOAT_H 1
 
 #undef FLT_ROUNDS
 #define FLT_ROUNDS 1
diff --git a/iso646.h b/iso646.h
index 7f9dc9d..159d6ef 100644
--- a/iso646.h
+++ b/iso646.h
@@ -12,8 +12,8 @@
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-#ifndef __FSTD_HDRS_ISO646_H
-#define __FSTD_HDRS_ISO646_H 1
+#ifndef __FREESTND_C_HDRS_ISO646_H
+#define __FREESTND_C_HDRS_ISO646_H 1
 
 #ifndef __cplusplus
 
diff --git a/limits.h b/limits.h
index 5d14b49..c26dec0 100644
--- a/limits.h
+++ b/limits.h
@@ -12,8 +12,8 @@
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-#ifndef __FSTD_HDRS_LIMITS_H
-#define __FSTD_HDRS_LIMITS_H 1
+#ifndef __FREESTND_C_HDRS_LIMITS_H
+#define __FREESTND_C_HDRS_LIMITS_H 1
 
 #undef CHAR_BIT
 #define CHAR_BIT __CHAR_BIT__
diff --git a/stdalign.h b/stdalign.h
index 7aab6a3..fc4f066 100644
--- a/stdalign.h
+++ b/stdalign.h
@@ -12,8 +12,8 @@
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-#ifndef __FSTD_HDRS_STDALIGN_H
-#define __FSTD_HDRS_STDALIGN_H 1
+#ifndef __FREESTND_C_HDRS_STDALIGN_H
+#define __FREESTND_C_HDRS_STDALIGN_H 1
 
 #ifndef __cplusplus
 
diff --git a/stdarg.h b/stdarg.h
index b158794..bcd411f 100644
--- a/stdarg.h
+++ b/stdarg.h
@@ -12,8 +12,8 @@
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-#ifndef __FSTD_HDRS_STDARG_H
-#define __FSTD_HDRS_STDARG_H 1
+#ifndef __FREESTND_C_HDRS_STDARG_H
+#define __FREESTND_C_HDRS_STDARG_H 1
 
 typedef __builtin_va_list va_list;
 
diff --git a/stdbool.h b/stdbool.h
index b0e7320..ddb0b8f 100644
--- a/stdbool.h
+++ b/stdbool.h
@@ -12,8 +12,8 @@
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-#ifndef __FSTD_HDRS_STDBOOL_H
-#define __FSTD_HDRS_STDBOOL_H 1
+#ifndef __FREESTND_C_HDRS_STDBOOL_H
+#define __FREESTND_C_HDRS_STDBOOL_H 1
 
 #ifndef __cplusplus
 
diff --git a/stddef.h b/stddef.h
index adf4a32..2c739ff 100644
--- a/stddef.h
+++ b/stddef.h
@@ -12,8 +12,8 @@
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-#ifndef __FSTD_HDRS_STDDEF_H
-#define __FSTD_HDRS_STDDEF_H 1
+#ifndef __FREESTND_C_HDRS_STDDEF_H
+#define __FREESTND_C_HDRS_STDDEF_H 1
 
 typedef __SIZE_TYPE__ size_t;
 typedef __PTRDIFF_TYPE__ ptrdiff_t;
diff --git a/stdint.h b/stdint.h
index 7ff828a..4063eff 100644
--- a/stdint.h
+++ b/stdint.h
@@ -12,8 +12,8 @@
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-#ifndef __FSTD_HDRS_STDINT_H
-#define __FSTD_HDRS_STDINT_H 1
+#ifndef __FREESTND_C_HDRS_STDINT_H
+#define __FREESTND_C_HDRS_STDINT_H 1
 
 #ifdef __UINT8_TYPE__
 typedef __UINT8_TYPE__ uint8_t;
@@ -73,33 +73,33 @@ typedef __INTMAX_TYPE__ intmax_t;
 
 /* Clang and GCC have different mechanisms for INT32_C and friends. */
 #ifdef __clang__
-#   ifndef __FSTD_HDRS_C_JOIN
-#       define __FSTD_HDRS_C_EXPAND_JOIN(x, suffix) x ## suffix
-#       define __FSTD_HDRS_C_JOIN(x, suffix) __FSTD_HDRS_C_EXPAND_JOIN(x, suffix)
+#   ifndef __FREESTND_C_HDRS_C_JOIN
+#       define __FREESTND_C_HDRS_C_EXPAND_JOIN(x, suffix) x ## suffix
+#       define __FREESTND_C_HDRS_C_JOIN(x, suffix) __FREESTND_C_HDRS_C_EXPAND_JOIN(x, suffix)
 #   endif
 
 #   undef INT8_C
-#   define INT8_C(x) __FSTD_HDRS_C_JOIN(x, __INT8_C_SUFFIX__)
+#   define INT8_C(x) __FREESTND_C_HDRS_C_JOIN(x, __INT8_C_SUFFIX__)
 #   undef INT16_C
-#   define INT16_C(x) __FSTD_HDRS_C_JOIN(x, __INT16_C_SUFFIX__)
+#   define INT16_C(x) __FREESTND_C_HDRS_C_JOIN(x, __INT16_C_SUFFIX__)
 #   undef INT32_C
-#   define INT32_C(x) __FSTD_HDRS_C_JOIN(x, __INT32_C_SUFFIX__)
+#   define INT32_C(x) __FREESTND_C_HDRS_C_JOIN(x, __INT32_C_SUFFIX__)
 #   undef INT64_C
-#   define INT64_C(x) __FSTD_HDRS_C_JOIN(x, __INT64_C_SUFFIX__)
+#   define INT64_C(x) __FREESTND_C_HDRS_C_JOIN(x, __INT64_C_SUFFIX__)
 
 #   undef UINT8_C
-#   define UINT8_C(x) __FSTD_HDRS_C_JOIN(x, __UINT8_C_SUFFIX__)
+#   define UINT8_C(x) __FREESTND_C_HDRS_C_JOIN(x, __UINT8_C_SUFFIX__)
 #   undef UINT16_C
-#   define UINT16_C(x) __FSTD_HDRS_C_JOIN(x, __UINT16_C_SUFFIX__)
+#   define UINT16_C(x) __FREESTND_C_HDRS_C_JOIN(x, __UINT16_C_SUFFIX__)
 #   undef UINT32_C
-#   define UINT32_C(x) __FSTD_HDRS_C_JOIN(x, __UINT32_C_SUFFIX__)
+#   define UINT32_C(x) __FREESTND_C_HDRS_C_JOIN(x, __UINT32_C_SUFFIX__)
 #   undef UINT64_C
-#   define UINT64_C(x) __FSTD_HDRS_C_JOIN(x, __UINT64_C_SUFFIX__)
+#   define UINT64_C(x) __FREESTND_C_HDRS_C_JOIN(x, __UINT64_C_SUFFIX__)
 
 #   undef INTMAX_C
-#   define INTMAX_C(x) __FSTD_HDRS_C_JOIN(x, __INTMAX_C_SUFFIX__)
+#   define INTMAX_C(x) __FREESTND_C_HDRS_C_JOIN(x, __INTMAX_C_SUFFIX__)
 #   undef UINTMAX_C
-#   define UINTMAX_C(x) __FSTD_HDRS_C_JOIN(x, __UINTMAX_C_SUFFIX__)
+#   define UINTMAX_C(x) __FREESTND_C_HDRS_C_JOIN(x, __UINTMAX_C_SUFFIX__)
 #else
 #   undef INT8_C
 #   define INT8_C(x) __INT8_C(x)
diff --git a/stdnoreturn.h b/stdnoreturn.h
index e6044df..c498436 100644
--- a/stdnoreturn.h
+++ b/stdnoreturn.h
@@ -12,8 +12,8 @@
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-#ifndef __FSTD_HDRS_STDNORETURN_H
-#define __FSTD_HDRS_STDNORETURN_H 1
+#ifndef __FREESTND_C_HDRS_STDNORETURN_H
+#define __FREESTND_C_HDRS_STDNORETURN_H 1
 
 #ifndef __cplusplus