diff --git a/tests/hevm.py b/tests/hevm.py
index 5348c4964f..0cb778fc91 100644
--- a/tests/hevm.py
+++ b/tests/hevm.py
@@ -32,11 +32,12 @@ def _prep_hevm_venom(venom_source_code, verbose=False):
 # small class to ensure correct function traversal order and help with
 # allocation
 class _FunctionVisitor:
-    num_calldataloads = 0
     visited: set
+    num_calldataloads: int
 
     def __init__(self):
         self.visited = set()
+        self.num_calldataloads = 0
 
 
 def _prep_hevm_venom_ctx(ctx, verbose=False):
diff --git a/tests/unit/hevm/test_hevm_negative.py b/tests/unit/hevm/test_hevm_negative.py
index f95793a5c6..734277d06b 100644
--- a/tests/unit/hevm/test_hevm_negative.py
+++ b/tests/unit/hevm/test_hevm_negative.py
@@ -1,6 +1,6 @@
 import pytest
 
-from tests.hevm import hevm_check_venom, hevm_raises
+from tests.hevm import _prep_hevm_venom, hevm_check_venom, hevm_raises
 
 """
 Test that the hevm harness can actually detect faults,
@@ -11,6 +11,41 @@
 pytestmark = pytest.mark.hevm
 
 
+def test_hevm_source_limit():
+    # 8 symbolic sources should work (hevm limit: 256 bytes of calldata)
+    code8 = """
+    main:
+        %1 = source
+        %2 = source
+        %3 = source
+        %4 = source
+        %5 = source
+        %6 = source
+        %7 = source
+        %8 = source
+        sink %1
+    """
+    result = _prep_hevm_venom(code8)
+    assert isinstance(result, str)
+
+    # 9 sources should fail the harness limit assertion
+    code9 = """
+    main:
+        %1 = source
+        %2 = source
+        %3 = source
+        %4 = source
+        %5 = source
+        %6 = source
+        %7 = source
+        %8 = source
+        %9 = source
+        sink %1
+    """
+    with pytest.raises(AssertionError):
+        _prep_hevm_venom(code9)
+
+
 def test_hevm_simple():
     code1 = """
     main: