diff --git a/src/strconv/atof.go b/src/strconv/atof.go
index 9010a66ca8..57556c7047 100644
--- a/src/strconv/atof.go
+++ b/src/strconv/atof.go
@@ -689,7 +689,7 @@ func atof64(s string) (f float64, n int, err error) {
 // as their respective special floating point values. It ignores case when matching.
 func ParseFloat(s string, bitSize int) (float64, error) {
 	f, n, err := parseFloatPrefix(s, bitSize)
-	if err == nil && n != len(s) {
+	if n != len(s) && (err == nil || err.(*NumError).Err != ErrSyntax) {
 		return 0, syntaxError(fnParseFloat, s)
 	}
 	return f, err
diff --git a/src/strconv/atof_test.go b/src/strconv/atof_test.go
index 3c058b9be5..aa587a473c 100644
--- a/src/strconv/atof_test.go
+++ b/src/strconv/atof_test.go
@@ -342,6 +342,9 @@ var atoftests = []atofTest{
 	{"0x12.345p-_12", "0", ErrSyntax},
 	{"0x12.345p+1__2", "0", ErrSyntax},
 	{"0x12.345p+12_", "0", ErrSyntax},
+
+	{"1e100x", "0", ErrSyntax},
+	{"1e1000x", "0", ErrSyntax},
 }
 
 var atof32tests = []atofTest{