diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 9541520..71d8426 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -239,7 +239,8 @@
 
 #define __BIONIC_FORTIFY_UNKNOWN_SIZE ((size_t) -1)
 
-#if defined(_FORTIFY_SOURCE) && _FORTIFY_SOURCE > 0 && defined(__OPTIMIZE__) && __OPTIMIZE__ > 0
+#if defined(_FORTIFY_SOURCE) && _FORTIFY_SOURCE > 0 && \
+      (defined(__clang__) || (defined(__OPTIMIZE__) && __OPTIMIZE__ > 0))
 #  define __BIONIC_FORTIFY 1
 #  if _FORTIFY_SOURCE == 2
 #    define __bos_level 1
@@ -281,8 +282,7 @@
 #define __pass_object_size __pass_object_size_n(__bos_level)
 #define __pass_object_size0 __pass_object_size_n(0)
 
-/* FIXME: This should be __BIONIC_FORTIFY, but we don't enable FORTIFY in -O0. */
-#if (defined(_FORTIFY_SOURCE) && _FORTIFY_SOURCE > 0) || defined(__BIONIC_DECLARE_FORTIFY_HELPERS)
+#if defined(__BIONIC_FORTIFY) || defined(__BIONIC_DECLARE_FORTIFY_HELPERS)
 #  define __BIONIC_INCLUDE_FORTIFY_HEADERS 1
 #endif
 
diff --git a/tools/versioner/src/Driver.cpp b/tools/versioner/src/Driver.cpp
index a094818..8a8e00a 100644
--- a/tools/versioner/src/Driver.cpp
+++ b/tools/versioner/src/Driver.cpp
@@ -119,7 +119,14 @@
 
   cmd.push_back("-DANDROID");
   cmd.push_back("-D__ANDROID_API__="s + std::to_string(type.api_level));
+  // FIXME: Re-enable FORTIFY properly once our clang in external/ is new enough
+  // to support diagnose_if without giving us syntax errors.
+#if 0
   cmd.push_back("-D_FORTIFY_SOURCE=2");
+#else
+  cmd.push_back("-D_FORTIFY_SOURCE=0");
+  cmd.push_back("-D__BIONIC_DECLARE_FORTIFY_HELPERS");
+#endif
   cmd.push_back("-D_GNU_SOURCE");
   cmd.push_back("-D_FILE_OFFSET_BITS="s + std::to_string(type.file_offset_bits));