diff --git a/builtin-update-index.c b/builtin-update-index.c
index 0620e779b0..a3c0a455ae 100644
--- a/builtin-update-index.c
+++ b/builtin-update-index.c
@@ -112,11 +112,13 @@ static int add_file_to_cache(const char *path)
 	ce->ce_mode = create_ce_mode(st.st_mode);
 	if (!trust_executable_bit) {
 		/* If there is an existing entry, pick the mode bits
-		 * from it.
+		 * from it, otherwise force to 644.
 		 */
 		int pos = cache_name_pos(path, namelen);
 		if (0 <= pos)
 			ce->ce_mode = active_cache[pos]->ce_mode;
+		else
+			ce->ce_mode = create_ce_mode(S_IFREG | 0644);
 	}
 
 	if (index_path(ce->sha1, path, &st, !info_only))
diff --git a/read-cache.c b/read-cache.c
index 20c9d494ac..97c38670b4 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -347,11 +347,13 @@ int add_file_to_index(const char *path, int verbose)
 	ce->ce_mode = create_ce_mode(st.st_mode);
 	if (!trust_executable_bit) {
 		/* If there is an existing entry, pick the mode bits
-		 * from it.
+		 * from it, otherwise force to 644.
 		 */
 		int pos = cache_name_pos(path, namelen);
 		if (pos >= 0)
 			ce->ce_mode = active_cache[pos]->ce_mode;
+		else
+			ce->ce_mode = create_ce_mode(S_IFREG | 0644);
 	}
 
 	if (index_path(ce->sha1, path, &st, 1))
diff --git a/t/t3700-add.sh b/t/t3700-add.sh
index 6cd05c3d90..d36f22d7de 100755
--- a/t/t3700-add.sh
+++ b/t/t3700-add.sh
@@ -19,4 +19,26 @@ test_expect_success \
     'Test that "git-add -- -q" works' \
     'touch -- -q && git-add -- -q'
 
+test_expect_success \
+	'git-add: Test that executable bit is not used if core.filemode=0' \
+	'git repo-config core.filemode 0 &&
+	 echo foo >xfoo1 &&
+	 chmod 755 xfoo1 &&
+	 git-add xfoo1 &&
+	 case "`git-ls-files --stage xfoo1`" in
+	 100644" "*xfoo1) echo ok;;
+	 *) echo fail; git-ls-files --stage xfoo1; exit 1;;
+	 esac'
+
+test_expect_success \
+	'git-update-index --add: Test that executable bit is not used...' \
+	'git repo-config core.filemode 0 &&
+	 echo foo >xfoo2 &&
+	 chmod 755 xfoo2 &&
+	 git-add xfoo2 &&
+	 case "`git-ls-files --stage xfoo2`" in
+	 100644" "*xfoo2) echo ok;;
+	 *) echo fail; git-ls-files --stage xfoo2; exit 1;;
+	 esac'
+
 test_done