diff --git a/mrbgems/mruby-compiler/core/parse.y b/mrbgems/mruby-compiler/core/parse.y
index 9e3f35bd7..7039c4507 100644
--- a/mrbgems/mruby-compiler/core/parse.y
+++ b/mrbgems/mruby-compiler/core/parse.y
@@ -4856,7 +4856,7 @@ parse_string(parser_state *p)
             --len;
           }
         }
-        if ((len-1 == hinf->term_len) && (strncmp(s, hinf->term, len-1) == 0)) {
+        if (hinf->term_len > 0 && len-1 == hinf->term_len && strncmp(s, hinf->term, len-1) == 0) {
           heredoc_remove_indent(p, hinf);
           return tHEREDOC_END;
         }
diff --git a/mrbgems/mruby-compiler/core/y.tab.c b/mrbgems/mruby-compiler/core/y.tab.c
index 2ba45e94e..826be9d70 100644
--- a/mrbgems/mruby-compiler/core/y.tab.c
+++ b/mrbgems/mruby-compiler/core/y.tab.c
@@ -11087,7 +11087,7 @@ parse_string(parser_state *p)
             --len;
           }
         }
-        if ((len-1 == hinf->term_len) && (strncmp(s, hinf->term, len-1) == 0)) {
+        if (hinf->term_len > 0 && len-1 == hinf->term_len && strncmp(s, hinf->term, len-1) == 0) {
           heredoc_remove_indent(p, hinf);
           return tHEREDOC_END;
         }