diff --git a/sysdeps/alpha/fpu/bits/mathinline.h b/sysdeps/alpha/fpu/bits/mathinline.h
index 250171eeb4..5378a181c6 100644
--- a/sysdeps/alpha/fpu/bits/mathinline.h
+++ b/sysdeps/alpha/fpu/bits/mathinline.h
@@ -23,7 +23,7 @@
 # error "Never use <bits/mathinline.h> directly; include <math.h> instead."
 #endif
 
-#ifdef __cplusplus
+#ifndef __extern_inline
 # define __MATH_INLINE __inline
 #else
 # define __MATH_INLINE __extern_inline