diff --git a/packfile.c b/packfile.c
index 6ab5233613..bfe76b2119 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1764,12 +1764,10 @@ void *unpack_entry(struct repository *r, struct packed_git *p, off_t obj_offset,
 		void *external_base = NULL;
 		unsigned long delta_size, base_size = size;
 		int i;
+		off_t base_obj_offset = obj_offset;
 
 		data = NULL;
 
-		if (base)
-			add_delta_base_cache(p, obj_offset, base, base_size, type);
-
 		if (!base) {
 			/*
 			 * We're probably in deep shit, but let's try to fetch
@@ -1807,24 +1805,33 @@ void *unpack_entry(struct repository *r, struct packed_git *p, off_t obj_offset,
 			      "at offset %"PRIuMAX" from %s",
 			      (uintmax_t)curpos, p->pack_name);
 			data = NULL;
-			free(external_base);
-			continue;
+		} else {
+			data = patch_delta(base, base_size, delta_data,
+					   delta_size, &size);
+
+			/*
+			 * We could not apply the delta; warn the user, but
+			 * keep going. Our failure will be noticed either in
+			 * the next iteration of the loop, or if this is the
+			 * final delta, in the caller when we return NULL.
+			 * Those code paths will take care of making a more
+			 * explicit warning and retrying with another copy of
+			 * the object.
+			 */
+			if (!data)
+				error("failed to apply delta");
 		}
 
-		data = patch_delta(base, base_size,
-				   delta_data, delta_size,
-				   &size);
-
 		/*
-		 * We could not apply the delta; warn the user, but keep going.
-		 * Our failure will be noticed either in the next iteration of
-		 * the loop, or if this is the final delta, in the caller when
-		 * we return NULL. Those code paths will take care of making
-		 * a more explicit warning and retrying with another copy of
-		 * the object.
+		 * We delay adding `base` to the cache until the end of the loop
+		 * because unpack_compressed_entry() momentarily releases the
+		 * obj_read_mutex, giving another thread the chance to access
+		 * the cache. Therefore, if `base` was already there, this other
+		 * thread could free() it (e.g. to make space for another entry)
+		 * before we are done using it.
 		 */
-		if (!data)
-			error("failed to apply delta");
+		if (!external_base)
+			add_delta_base_cache(p, base_obj_offset, base, base_size, type);
 
 		free(delta_data);
 		free(external_base);