diff --git a/Include/pymath.h b/Include/pymath.h
index 13f95b4..9e0f46f 100644
--- a/Include/pymath.h
+++ b/Include/pymath.h
@@ -87,7 +87,7 @@
  * Note: PC/pyconfig.h defines Py_IS_NAN as _isnan
  */
 #ifndef Py_IS_NAN
-#ifdef HAVE_DECL_ISNAN
+#ifdef HAVE_DECL_ISNAN && HAVE_DECL_ISNAN == 1
 #define Py_IS_NAN(X) isnan(X)
 #else
 #define Py_IS_NAN(X) ((X) != (X))
@@ -104,7 +104,7 @@
  * Note: PC/pyconfig.h defines Py_IS_INFINITY as _isinf
  */
 #ifndef Py_IS_INFINITY
-#ifdef HAVE_DECL_ISINF
+#ifdef HAVE_DECL_ISINF && HAVE_DECL_ISINF == 1
 #define Py_IS_INFINITY(X) isinf(X)
 #else
 #define Py_IS_INFINITY(X) ((X) && (X)*0.5 == (X))