diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 0e64b4159c4f8a81ed1d346631f6c3894297ceeb..fe5c77f54cf556547a3c7d90ebc77ef841ca6593 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -266,6 +266,15 @@ static int batch_objects(struct batch_options *opt)
 	strbuf_expand(&buf, opt->format, expand_format, &data);
 	data.mark_query = 0;
 
+	/*
+	 * We are going to call get_sha1 on a potentially very large number of
+	 * objects. In most large cases, these will be actual object sha1s. The
+	 * cost to double-check that each one is not also a ref (just so we can
+	 * warn) ends up dwarfing the actual cost of the object lookups
+	 * themselves. We can work around it by just turning off the warning.
+	 */
+	warn_on_object_refname_ambiguity = 0;
+
 	while (strbuf_getline(&buf, stdin, '\n') != EOF) {
 		char *p;
 		int error;
diff --git a/cache.h b/cache.h
index f2915509a64b828f1b0bd78cecb9f091577ac874..dc99366a2e643a6217d474495611b09cfc6db20f 100644
--- a/cache.h
+++ b/cache.h
@@ -554,6 +554,7 @@ extern int assume_unchanged;
 extern int prefer_symlink_refs;
 extern int log_all_ref_updates;
 extern int warn_ambiguous_refs;
+extern int warn_on_object_refname_ambiguity;
 extern int shared_repository;
 extern const char *apply_default_whitespace;
 extern const char *apply_default_ignorewhitespace;
diff --git a/environment.c b/environment.c
index e2e75c16602d8e5841c2461defaba7b9866115d8..1a99e472516b2d67cf6f10dcd33589e3c9fd3d46 100644
--- a/environment.c
+++ b/environment.c
@@ -22,6 +22,7 @@ int prefer_symlink_refs;
 int is_bare_repository_cfg = -1; /* unspecified */
 int log_all_ref_updates = -1; /* unspecified */
 int warn_ambiguous_refs = 1;
+int warn_on_object_refname_ambiguity = 1;
 int repository_format_version;
 const char *git_commit_encoding;
 const char *git_log_output_encoding;
diff --git a/sha1_name.c b/sha1_name.c
index a1e0f804dc1844a0df936bc48bcdc4839c612566..c1957f35c182af9bf91658fa37602cf4071c7c37 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -451,13 +451,15 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 	int at, reflog_len;
 
 	if (len == 40 && !get_sha1_hex(str, sha1)) {
-		refs_found = dwim_ref(str, len, tmp_sha1, &real_ref);
-		if (refs_found > 0 && warn_ambiguous_refs) {
-			warning(warn_msg, len, str);
-			if (advice_object_name_warning)
-				fprintf(stderr, "%s\n", _(object_name_msg));
+		if (warn_on_object_refname_ambiguity) {
+			refs_found = dwim_ref(str, len, tmp_sha1, &real_ref);
+			if (refs_found > 0 && warn_ambiguous_refs) {
+				warning(warn_msg, len, str);
+				if (advice_object_name_warning)
+					fprintf(stderr, "%s\n", _(object_name_msg));
+			}
+			free(real_ref);
 		}
-		free(real_ref);
 		return 0;
 	}