1 files changed, 3 insertions, 2 deletions
diff --git a/math.c b/math.c
index 98b327272b..276b2cbc49 100644
--- a/math.c
+++ b/math.c
@@ -14,8 +14,9 @@
 #include <math.h>
 #include <errno.h>
 
-#if defined(HAVE_SIGNBIT) && defined(__GNUC__) && defined(__sun__)
-    extern int signbit(double x);
+#if defined(HAVE_SIGNBIT) && defined(__GNUC__) && defined(__sun__) && \
+    !defined(signbit)
+    extern int signbit(double);
 #endif
 
 #define numberof(array) (int)(sizeof(array) / sizeof((array)[0]))