diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c
index 37f24e33857..79295d43ddf 100644
--- a/src/backend/utils/adt/numeric.c
+++ b/src/backend/utils/adt/numeric.c
@@ -6378,22 +6378,15 @@ int4_sum(PG_FUNCTION_ARGS)
 	int64		oldsum;
 	int64		newval;
 
+	/* Return the left input unchanged if right input is null. */
+	if (PG_ARGISNULL(1))
+		PG_RETURN_INPUT(0);
+
 	if (PG_ARGISNULL(0))
-	{
-		/* No non-null input seen so far... */
-		if (PG_ARGISNULL(1))
-			PG_RETURN_NULL();	/* still no non-null */
-		/* This is the first non-null input. */
-		newval = (int64) PG_GETARG_INT32(1);
-		PG_RETURN_INT64(newval);
-	}
+		PG_RETURN_INT64((int64) PG_GETARG_INT32(1));
 
 	oldsum = PG_GETARG_INT64(0);
 
-	/* Leave sum unchanged if new input is null. */
-	if (PG_ARGISNULL(1))
-		PG_RETURN_INT64(oldsum);
-
 	/* OK to do the addition. */
 	newval = oldsum + (int64) PG_GETARG_INT32(1);
 
diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index 04b7914095f..e3c2b3ac686 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -349,6 +349,16 @@ extern varlena *pg_detoast_datum_packed(varlena *datum);
 /* A few internal functions return void (which is not the same as NULL!) */
 #define PG_RETURN_VOID()	 return (Datum) 0
 
+/*
+ * A shortcut to allow functions to return the value of the give input
+ * parameter, NULL if that parameter was NULL and the value of the parameter
+ * otherwise.  The caller is responsible for ensuring the types match.
+ */
+#define PG_RETURN_INPUT(n)  do { \
+		fcinfo->isnull = fcinfo->args[n].isnull; \
+		return fcinfo->args[n].value; \
+	} while (0)
+
 /* Macros for returning results of standard types */
 
 #define PG_RETURN_DATUM(x)	 return (x)