diff --git a/src/strconv/atof.go b/src/strconv/atof.go
index c1e9907e09..28ad094080 100644
--- a/src/strconv/atof.go
+++ b/src/strconv/atof.go
@@ -55,7 +55,11 @@ func special(s string) (f float64, n int, ok bool) {
 		fallthrough
 	case 'i', 'I':
 		n := commonPrefixLenIgnoreCase(s, "infinity")
-		// both "inf" and "infinity" are ok
+		// Anything longer than "inf" is ok, but if we
+		// don't have "infinity", only consume "inf".
+		if 3 < n && n < 8 {
+			n = 3
+		}
 		if n == 3 || n == 8 {
 			return math.Inf(sign), nsign + n, true
 		}
diff --git a/src/strconv/atof_test.go b/src/strconv/atof_test.go
index 8201e75af6..c30cb2e0fe 100644
--- a/src/strconv/atof_test.go
+++ b/src/strconv/atof_test.go
@@ -486,8 +486,9 @@ func TestParseFloatPrefix(t *testing.T) {
 			continue
 		}
 		// Adding characters that do not extend a number should not invalidate it.
-		// Test a few.
-		for _, suffix := range []string{" ", "q", "+", "-", "<", "=", ">", "(", ")"} {
+		// Test a few. The "i" and "init" cases test that we accept "infi", "infinit"
+		// correctly as "inf" with suffix.
+		for _, suffix := range []string{" ", "q", "+", "-", "<", "=", ">", "(", ")", "i", "init"} {
 			in := test.in + suffix
 			_, n, err := ParseFloatPrefix(in, 64)
 			if err != nil {