diff --git a/src/common/classes/FpeControl.h b/src/common/classes/FpeControl.h
index 7f50fc4aa6..b3f0b66d4f 100644
--- a/src/common/classes/FpeControl.h
+++ b/src/common/classes/FpeControl.h
@@ -222,6 +222,14 @@ inline bool isinf(double x)
 {
 	return (!_finite (x) && !isnan(x));
 }
+#else
+#ifndef isinf
+template <typename F>
+inline bool isinf(F x)
+{
+	return !isnan(x) && isnan(x - x);
+}
+#endif // isinf
 #endif // WIN_NT
 
 namespace Firebird {