diff --git a/simgear/compiler.h b/simgear/compiler.h
index cfa91f86..5f02adb2 100644
--- a/simgear/compiler.h
+++ b/simgear/compiler.h
@@ -138,8 +138,8 @@ inline int (isnan)(double r) { return !(r <= 0 || r >= 0); }
     // any C++ header file undefines isinf and isnan
     // so this should be included before <iostream>
     // the functions are STILL in libm (libSystem on mac os x)
-extern "C" int isnan (double);
-extern "C" int isinf (double);
+extern "C" int (isnan)(double);
+extern "C" int (isinf)(double);
 #    endif
 #  else
 inline int (isnan)(double r) { return !(r <= 0 || r >= 0); }