diff --git a/strbuf.c b/strbuf.c
index d76f0aed8..258650ccb 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -470,9 +470,15 @@ int strbuf_getwholeline(struct strbuf *sb, FILE *fp, int term)
 	if (errno == ENOMEM)
 		die("Out of memory, getdelim failed");
 
-	/* Restore slopbuf that we moved out of the way before */
+	/*
+	 * Restore strbuf invariants; if getdelim left us with a NULL pointer,
+	 * we can just re-init, but otherwise we should make sure that our
+	 * length is empty, and that the result is NUL-terminated.
+	 */
 	if (!sb->buf)
 		strbuf_init(sb, 0);
+	else
+		strbuf_reset(sb);
 	return EOF;
 }
 #else
diff --git a/t/t9300-fast-import.sh b/t/t9300-fast-import.sh
index 14a938402..95c70ed43 100755
--- a/t/t9300-fast-import.sh
+++ b/t/t9300-fast-import.sh
@@ -55,6 +55,10 @@ test_expect_success 'empty stream succeeds' '
 	git fast-import </dev/null
 '
 
+test_expect_success 'truncated stream complains' '
+	echo "tag foo" | test_must_fail git fast-import
+'
+
 test_expect_success 'A: create pack from stdin' '
 	test_tick &&
 	cat >input <<-INPUT_END &&