diff --git a/mypy/build.py b/mypy/build.py
index 0201cd2c2186..bfd557c65174 100644
--- a/mypy/build.py
+++ b/mypy/build.py
@@ -825,8 +825,21 @@ def _load_json_file(file: str, manager: BuildManager,
         manager.log(log_error + file)
         return None
     manager.trace(log_sucess + data.rstrip())
-    result = json.loads(data)  # TODO: Errors
-    return result
+    try:
+        result = json.loads(data)
+    except ValueError:  # TODO: JSONDecodeError in 3.5
+        manager.errors.set_file(file, None)
+        manager.errors.report(-1, -1,
+                              "Error reading JSON file;"
+                              " you likely have a bad cache.\n"
+                              "Try removing the {cache_dir} directory"
+                              " and run mypy again.".format(
+                                  cache_dir=manager.options.cache_dir
+                              ),
+                              blocker=True)
+        return None
+    else:
+        return result
 
 
 def _cache_dir_prefix(manager: BuildManager) -> str: