diff --git a/src/backend/access/hash/hashfunc.c b/src/backend/access/hash/hashfunc.c
index 89c2712b4c4..b2422260f61 100644
--- a/src/backend/access/hash/hashfunc.c
+++ b/src/backend/access/hash/hashfunc.c
@@ -26,7 +26,13 @@
 
 #include "postgres.h"
 
+#ifdef _MSC_VER
+#include <float.h>				/* for _isnan */
+#endif
+#include <math.h>
+
 #include "access/hash.h"
+#include "utils/builtins.h"
 
 
 /* Note: this is used for both "char" and boolean datatypes */
@@ -94,6 +100,14 @@ hashfloat4(PG_FUNCTION_ARGS)
 	if (key == (float4) 0)
 		PG_RETURN_UINT32(0);
 
+	/*
+	 * Similarly, NaNs can have different bit patterns but they should all
+	 * compare as equal.  For backwards-compatibility reasons we force them to
+	 * have the hash value of a standard NaN.
+	 */
+	if (isnan(key))
+		key = get_float4_nan();
+
 	/*
 	 * To support cross-type hashing of float8 and float4, we want to return
 	 * the same hash value hashfloat8 would produce for an equal float8 value.
@@ -119,6 +133,14 @@ hashfloat8(PG_FUNCTION_ARGS)
 	if (key == (float8) 0)
 		PG_RETURN_UINT32(0);
 
+	/*
+	 * Similarly, NaNs can have different bit patterns but they should all
+	 * compare as equal.  For backwards-compatibility reasons we force them to
+	 * have the hash value of a standard NaN.
+	 */
+	if (isnan(key))
+		key = get_float8_nan();
+
 	return hash_any((unsigned char *) &key, sizeof(key));
 }