diff --git a/brownie/project/compiler/utils.py b/brownie/project/compiler/utils.py
index 784071239..8694d9cd7 100644
--- a/brownie/project/compiler/utils.py
+++ b/brownie/project/compiler/utils.py
@@ -8,10 +8,12 @@
 
 def expand_source_map(source_map_str: str) -> List:
     # Expands the compressed sourceMap supplied by solc into a list of lists
-
-    if not isinstance(source_map_str, str):
-        # NOTE: why do we need this?
+'
+    if isinstance(source_map_str, dict):
+        # NOTE: vyper >= 0.4 gives us a dict that contains the source map
         source_map_str = source_map_str["pc_pos_map_compressed"]
+    if not isinstance(source_map_str, str):
+        raise TypeError(source_map_str)
 
     source_map: List = [_expand_row(i) if i else None for i in source_map_str.split(";")]
     for i, value in enumerate(source_map[1:], 1):