diff --git a/src/pk_core.c b/src/pk_core.c
index afb65a7..071f3d1 100644
--- a/src/pk_core.c
+++ b/src/pk_core.c
@@ -1302,7 +1302,11 @@ bool varContains(PKVM* vm, Var elem, Var container) {
       return false;
     } break;
 
-    case OBJ_MAP:
+    case OBJ_MAP: {
+      Map* map = (Map*)AS_OBJ(container);
+      return !IS_UNDEF(mapGet(map, elem));
+    } break;
+
     case OBJ_RANGE:
     case OBJ_SCRIPT:
     case OBJ_FUNC:
diff --git a/tests/lang/basics.pk b/tests/lang/basics.pk
index 28633c8..ccb7d05 100644
--- a/tests/lang/basics.pk
+++ b/tests/lang/basics.pk
@@ -31,6 +31,8 @@ l3 = l2 + l1 + l2; assert(l3 == [1,1,2,3,1,1,1,2,3])
 assert(!('abc' in 'a'))
 assert(42 in [12, 42, 3.14])
 assert(!('a' in ['abc']))
+assert('key' in {'key':'value'})
+assert(!('foo' in {'bar':'baz'}))
 
 ## Builtin functions tests.
 assert(to_string(42) == '42')