diff --git a/sprintf.c b/sprintf.c
index 4fa531d53e..1d3b3e0d07 100644
--- a/sprintf.c
+++ b/sprintf.c
@@ -1165,7 +1165,9 @@ ruby_vsprintf0(VALUE result, char *p, const char *fmt, va_list ap)
     RBASIC_SET_CLASS_RAW(result, klass);
     p = RSTRING_PTR(result);
     long blen = (char *)f._p - p;
-    if (scanned < blen) {
+
+    coderange = ENC_CODERANGE(result);
+    if (coderange != ENC_CODERANGE_UNKNOWN && scanned < blen) {
         rb_str_coderange_scan_restartable(p + scanned, p + blen, rb_enc_get(result), &coderange);
         ENC_CODERANGE_SET(result, coderange);
     }
diff --git a/strftime.c b/strftime.c
index 906e8360a9..edaa9f02ce 100644
--- a/strftime.c
+++ b/strftime.c
@@ -932,6 +932,7 @@ rb_strftime(const char *format, size_t format_len, rb_encoding *enc,
 	    VALUE time, const struct vtm *vtm, VALUE timev, int gmt)
 {
 	VALUE result = rb_enc_str_new(0, 0, enc);
+	ENC_CODERANGE_CLEAR(result);
 	return rb_strftime_with_timespec(result, format, format_len, enc,
 					 time, vtm, timev, NULL, gmt,
 					 strftime_size_limit(format_len));
@@ -942,6 +943,7 @@ rb_strftime_timespec(const char *format, size_t format_len, rb_encoding *enc,
 		     VALUE time, const struct vtm *vtm, struct timespec *ts, int gmt)
 {
 	VALUE result = rb_enc_str_new(0, 0, enc);
+	ENC_CODERANGE_CLEAR(result);
 	return rb_strftime_with_timespec(result, format, format_len, enc,
 					 time, vtm, Qnil, ts, gmt,
 					 strftime_size_limit(format_len));