diff --git a/grep.c b/grep.c
index ac34bfeafb..2f8b9553df 100644
--- a/grep.c
+++ b/grep.c
@@ -1735,7 +1735,8 @@ static int grep_source_1(struct grep_opt *opt, struct grep_source *gs, int colle
 				peek_eol = end_of_line(peek_bol, &peek_left);
 			}
 
-			if (match_funcname(opt, gs, peek_bol, peek_eol))
+			if (peek_bol >= gs->buf + gs->size ||
+			    match_funcname(opt, gs, peek_bol, peek_eol))
 				show_function = 0;
 		}
 		if (show_function ||
diff --git a/t/t7810-grep.sh b/t/t7810-grep.sh
index 875dcfd98f..af2cf2f78a 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -31,6 +31,7 @@ int main(int argc, const char **argv)
 	return 0;
 	/* char ?? */
 }
+
 EOF
 
 test_expect_success setup '