diff --git a/ext/standard/filters.c b/ext/standard/filters.c
index 7115c534b06..cd92c6e2dcd 100644
--- a/ext/standard/filters.c
+++ b/ext/standard/filters.c
@@ -922,7 +922,7 @@ static php_conv_err_t php_conv_qprint_encode_convert(php_conv_qprint_encode *ins
 			line_ccnt--;
 			CONSUME_CHAR(ps, icnt, lb_ptr, lb_cnt);
 		} else {
-			if (line_ccnt < 4) {
+			if (line_ccnt < 4 && inst->lbchars != NULL) {
 				if (ocnt < inst->lbchars_len + 1) {
 					err = PHP_CONV_ERR_TOO_BIG;
 					break;
diff --git a/ext/standard/tests/filters/bug77231.phpt b/ext/standard/tests/filters/bug77231.phpt
new file mode 100644
index 00000000000..17967ee80fc
--- /dev/null
+++ b/ext/standard/tests/filters/bug77231.phpt
@@ -0,0 +1,11 @@
+--TEST--
+Bug #77231 (Segfault when using convert.quoted-printable-encode filter)
+--FILE--
+<?php
+var_dump(file(urldecode('php://filter/convert.quoted-printable-encode/resource=data://,%bfAAAAAAAAFAAAAAAAAAAAAAA%ff%ff%ff%ff%ff%ff%ff%ffAAAAAAAAAAAAAAAAAAAAAAAA')));
+?>
+--EXPECT--
+array(1) {
+  [0]=>
+  string(74) "=BFAAAAAAAAFAAAAAAAAAAAAAA=FF=FF=FF=FF=FF=FF=FF=FFAAAAAAAAAAAAAAAAAAAAAAAA"
+}
\ No newline at end of file