diff --git a/gcc/real.h b/gcc/real.h
index 3e691ff436a..33b71670f84 100644
--- a/gcc/real.h
+++ b/gcc/real.h
@@ -137,6 +137,11 @@ extern double (atof) ();
 #define REAL_VALUE_ISINF(x) (target_isinf (x))
 #endif
 
+/* Determine whether a floating-point value X is a NaN. */
+#ifndef REAL_VALUE_ISNAN
+#define REAL_VALUE_ISNAN(x) (target_isnan (x))
+#endif
+
 /* Determine whether a floating-point value X is minus 0. */
 #ifndef REAL_VALUE_MINUS_ZERO
 #define REAL_VALUE_MINUS_ZERO(x) (target_minus_zero (x))