diff --git a/libc/Makefile b/libc/Makefile
index ede4fc3a..a2bd6c7e 100644
--- a/libc/Makefile
+++ b/libc/Makefile
@@ -10,7 +10,7 @@ endif
 CPUDIR:=$(CPU)
 
 CPPINCLUDES=-I preproc
-CPPFLAGS=-DLIBC_LIBRARY $(CPPINCLUDES)
+CPPFLAGS=-D__is_sortix_libc=1 $(CPPINCLUDES)
 FLAGS=-Wall -Wextra $(OPTLEVEL)
 CFLAGS=-std=gnu99
 CXXFLAGS=-std=gnu++11 -fno-exceptions -fno-rtti
diff --git a/libc/include/features.h b/libc/include/features.h
index 1f2dd038..f4fd6611 100644
--- a/libc/include/features.h
+++ b/libc/include/features.h
@@ -52,7 +52,7 @@
 #endif
 
 /* Sortix system components implicitly use the native API. */
-#if defined(LIBC_LIBRARY) || defined(SORTIX_KERNEL)
+#if __is_sortix_libc || defined(SORTIX_KERNEL)
 #define _SORTIX_SOURCE 1
 #endif
 
@@ -90,7 +90,7 @@
 #endif
 
 /* Provide the restrict keyword when building the C library. */
-#if !__HAS_RESTRICT && defined(LIBC_LIBRARY)
+#if !__HAS_RESTRICT && defined(__is_sortix_libc)
 #define restrict __restrict
 #undef __HAS_RESTRICT
 #define __HAS_RESTRICT 2
diff --git a/libc/include/stdint.h b/libc/include/stdint.h
index 437d83a8..23528829 100644
--- a/libc/include/stdint.h
+++ b/libc/include/stdint.h
@@ -32,7 +32,7 @@ __BEGIN_DECLS
 
 /* Only define these constant macros in C++ if requested. */
 #if !defined(__cplusplus) || defined(__STDC_CONSTANT_MACROS) || \
-    defined(LIBC_LIBRARY) || defined(SORTIX_KERNEL) /* TODO: HACK! */
+    defined(__is_sortix_libc) || defined(SORTIX_KERNEL) /* TODO: HACK! */
 
 #define INT8_C(c) __INT8_C(c)
 #define INT16_C(c) __INT16_C(c)
@@ -51,7 +51,7 @@ __BEGIN_DECLS
 
 /* Only define these limit macros in C++ if requested. */
 #if !defined(__cplusplus) || defined(__STDC_LIMIT_MACROS) || \
-    defined(LIBC_LIBRARY) || defined(SORTIX_KERNEL) /* TODO: HACK! */
+    defined(__is_sortix_libc) || defined(SORTIX_KERNEL) /* TODO: HACK! */
 
 #define INT8_MIN __INT8_MIN
 #define INT16_MIN __INT16_MIN
diff --git a/libc/include/stdio.h b/libc/include/stdio.h
index 493e6093..370e8e5a 100644
--- a/libc/include/stdio.h
+++ b/libc/include/stdio.h
@@ -177,7 +177,7 @@ int fcloseall(void);
 int fshutdown(FILE* fp);
 int fpipe(FILE* pipes[2]);
 /* Internally used by standard library. */
-#if defined(LIBC_LIBRARY)
+#if defined(__is_sortix_libc)
 extern FILE* _firstfile;
 #endif
 #endif
diff --git a/sortix/include/sortix/__/types.h b/sortix/include/sortix/__/types.h
index e89cb510..7e6bde0e 100644
--- a/sortix/include/sortix/__/types.h
+++ b/sortix/include/sortix/__/types.h
@@ -57,10 +57,10 @@ typedef int __ssize_t;
 typedef __uintptr_t __timer_t;
 typedef __SIZE_TYPE__ __socklen_t;
 
-#if defined(SORTIX_KERNEL) || defined(LIBC_LIBRARY)
+#if defined(SORTIX_KERNEL) || defined(__is_sortix_libc)
 #define OFF_MIN __OFF_MIN
 #endif
-#if defined(SORTIX_KERNEL) || defined(LIBC_LIBRARY)
+#if defined(SORTIX_KERNEL) || defined(__is_sortix_libc)
 #define OFF_MAX __OFF_MAX
 #endif