diff --git a/simde/simde-math.h b/simde/simde-math.h
index 403fcb93e..2df10c1df 100644
--- a/simde/simde-math.h
+++ b/simde/simde-math.h
@@ -175,7 +175,7 @@ SIMDE_DISABLE_UNWANTED_DIAGNOSTICS
   #endif
 #endif
 
-#if !defined(SIMDE_NANF)
+#if !defined(SIMDE_MATH_NANF)
   #if \
       HEDLEY_HAS_BUILTIN(__builtin_nanf) || \
       HEDLEY_GCC_VERSION_CHECK(3,3,0) || \