diff --git a/contrib/hstore/hstore_io.c b/contrib/hstore/hstore_io.c
index 6ce3047215..cd01b2fadd 100644
--- a/contrib/hstore/hstore_io.c
+++ b/contrib/hstore/hstore_io.c
@@ -12,6 +12,7 @@
 #include "libpq/pqformat.h"
 #include "utils/builtins.h"
 #include "utils/json.h"
+#include "utils/jsonapi.h"
 #include "utils/jsonb.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
@@ -1240,7 +1241,6 @@ hstore_to_json_loose(PG_FUNCTION_ARGS)
 	int			count = HS_COUNT(in);
 	char	   *base = STRPTR(in);
 	HEntry	   *entries = ARRPTR(in);
-	bool		is_number;
 	StringInfoData tmp,
 				dst;
 
@@ -1267,48 +1267,9 @@ hstore_to_json_loose(PG_FUNCTION_ARGS)
 			appendStringInfoString(&dst, "false");
 		else
 		{
-			is_number = false;
 			resetStringInfo(&tmp);
 			appendBinaryStringInfo(&tmp, HS_VAL(entries, base, i), HS_VALLEN(entries, i));
-
-			/*
-			 * don't treat something with a leading zero followed by another
-			 * digit as numeric - could be a zip code or similar
-			 */
-			if (tmp.len > 0 &&
-				!(tmp.data[0] == '0' &&
-				  isdigit((unsigned char) tmp.data[1])) &&
-				strspn(tmp.data, "+-0123456789Ee.") == tmp.len)
-			{
-				/*
-				 * might be a number. See if we can input it as a numeric
-				 * value. Ignore any actual parsed value.
-				 */
-				char	   *endptr = "junk";
-				long		lval;
-
-				lval = strtol(tmp.data, &endptr, 10);
-				(void) lval;
-				if (*endptr == '\0')
-				{
-					/*
-					 * strol man page says this means the whole string is
-					 * valid
-					 */
-					is_number = true;
-				}
-				else
-				{
-					/* not an int - try a double */
-					double		dval;
-
-					dval = strtod(tmp.data, &endptr);
-					(void) dval;
-					if (*endptr == '\0')
-						is_number = true;
-				}
-			}
-			if (is_number)
+			if (IsValidJsonNumber(tmp.data, tmp.len))
 				appendBinaryStringInfo(&dst, tmp.data, tmp.len);
 			else
 				escape_json(&dst, tmp.data);
diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index d2bf640e54..a576843234 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -173,6 +173,36 @@ lex_expect(JsonParseContext ctx, JsonLexContext *lex, JsonTokenType token)
 	 (c) == '_' || \
 	 IS_HIGHBIT_SET(c))
 
+/* utility function to check if a string is a valid JSON number */
+extern bool
+IsValidJsonNumber(const char * str, int len)
+{
+	bool		numeric_error;
+	JsonLexContext dummy_lex;
+
+
+	/*
+	 * json_lex_number expects a leading  '-' to have been eaten already.
+	 *
+	 * having to cast away the constness of str is ugly, but there's not much
+	 * easy alternative.
+	 */
+	if (*str == '-')
+	{
+		dummy_lex.input = (char *) str + 1;
+		dummy_lex.input_length = len - 1;
+	}
+	else
+	{
+		dummy_lex.input = (char *) str;
+		dummy_lex.input_length = len;
+	}
+
+	json_lex_number(&dummy_lex, dummy_lex.input, &numeric_error);
+
+	return ! numeric_error;
+}
+
 /*
  * Input.
  */
@@ -1338,8 +1368,6 @@ datum_to_json(Datum val, bool is_null, StringInfo result,
 {
 	char	   *outputstr;
 	text	   *jsontext;
-	bool		numeric_error;
-	JsonLexContext dummy_lex;
 
 	/* callers are expected to ensure that null keys are not passed in */
 	Assert( ! (key_scalar && is_null));
@@ -1376,25 +1404,14 @@ datum_to_json(Datum val, bool is_null, StringInfo result,
 			break;
 		case JSONTYPE_NUMERIC:
 			outputstr = OidOutputFunctionCall(outfuncoid, val);
-			if (key_scalar)
-			{
-				/* always quote keys */
-				escape_json(result, outputstr);
-			}
+			/*
+			 * Don't call escape_json for a non-key if it's a valid JSON
+			 * number.
+			 */
+			if (!key_scalar && IsValidJsonNumber(outputstr, strlen(outputstr)))
+				appendStringInfoString(result, outputstr);
 			else
-			{
-				/*
-				 * Don't call escape_json for a non-key if it's a valid JSON
-				 * number.
-				 */
-				dummy_lex.input = *outputstr == '-' ? outputstr + 1 : outputstr;
-				dummy_lex.input_length = strlen(dummy_lex.input);
-				json_lex_number(&dummy_lex, dummy_lex.input, &numeric_error);
-				if (!numeric_error)
-					appendStringInfoString(result, outputstr);
-				else
-					escape_json(result, outputstr);
-			}
+				escape_json(result, outputstr);
 			pfree(outputstr);
 			break;
 		case JSONTYPE_DATE:
diff --git a/src/include/utils/jsonapi.h b/src/include/utils/jsonapi.h
index df057121a1..4ae059bec6 100644
--- a/src/include/utils/jsonapi.h
+++ b/src/include/utils/jsonapi.h
@@ -117,4 +117,11 @@ extern JsonLexContext *makeJsonLexContextCstringLen(char *json,
 							 int len,
 							 bool need_escapes);
 
+/*
+ * Utility function to check if a string is a valid JSON number.
+ *
+ * str agrument does not need to be nul-terminated.
+ */
+extern bool IsValidJsonNumber(const char * str, int len);
+
 #endif   /* JSONAPI_H */