diff --git a/.github/workflows/main.yaml b/.github/workflows/main.yaml
index fa6705f..58c0781 100644
--- a/.github/workflows/main.yaml
+++ b/.github/workflows/main.yaml
@@ -41,7 +41,7 @@ jobs:
           - macOS-11
     needs: build
     env:
-      IVERILOG_REF: 7c5694e5163e905b7ba85096ae67e5f28862db48
+      IVERILOG_REF: eab37efb561259df7e27aa26f080a7b0f2ca48a1
     steps:
       - uses: actions/checkout@v1
       - name: Install Dependencies (macOS)
diff --git a/README.md b/README.md
index 4b464d1..fa445ae 100644
--- a/README.md
+++ b/README.md
@@ -39,7 +39,7 @@ All of sv2v's dependencies are free and open-source.
     * [Icarus Verilog](https://steveicarus.github.io/iverilog/) - for Verilog
       simulation
     * [shUnit2](https://github.com/kward/shunit2) - test framework
-    * Python (any version) - for generating certain test cases
+    * Python 3.x - for evaluating certain test cases
 
 
 ## Installation
diff --git a/test/lib/clean_vcd.py b/test/lib/clean_vcd.py
new file mode 100755
index 0000000..c23b7c3
--- /dev/null
+++ b/test/lib/clean_vcd.py
@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+
+import sys
+
+from collections import deque
+
+if __name__ == "__main__":
+    pending = deque()
+    replaced = {}
+    dumping = False
+
+    for line in sys.stdin:
+        # Find and drop dumped parameters.
+        if line.startswith("$var "):
+            parts = line.split()
+            should_drop = parts[1] == "parameter"
+            if not should_drop and not pending:
+                print(line, end="")
+                continue
+            ident_old = parts[3]
+            pending.append(ident_old)
+            if should_drop:
+                replaced[ident_old] = None
+                continue
+            ident_new = pending.popleft()
+            parts[3] = ident_new
+            replaced[ident_old] = ident_new
+            print(" ".join(parts))
+
+        # Pass through lines if we have no transformations to do.
+        elif line.startswith("$dump"):
+            dumping = True
+            print(line, end="")
+        elif line.startswith("$end"):
+            # dumping = False
+            print(line, end="")
+        elif not dumping or not replaced:
+            print(line, end="")
+        elif line[0] == "#":
+            print(line, end="")
+
+        # Rename dumped variables.
+        elif line.startswith("b"):
+            value, ident = line.split()
+            ident = replaced.get(ident, ident)
+            if ident is not None:
+                print(value, ident)
+        elif line[0] in "01xz":
+            value = line[0]
+            ident = line[1:-1]
+            ident = replaced.get(ident, ident)
+            if ident is not None:
+                print(value + ident)
+
+        else:
+            raise RuntimeError(f"Unhandled: {line.strip()}")
diff --git a/test/lib/functions.sh b/test/lib/functions.sh
index c37f63d..0322e5e 100644
--- a/test/lib/functions.sh
+++ b/test/lib/functions.sh
@@ -36,7 +36,7 @@ simulate() {
     $sim_prog > $sim_log
     assertTrue "simulating $1 failed" $?
     # remove the date from the VCD
-    sed -e "1,3d" < $sim_vcd_tmp > $sim_vcd
+    sed -e "1,3d" < $sim_vcd_tmp | $SCRIPT_DIR/clean_vcd.py > $sim_vcd
 }
 
 assertConverts() {
diff --git a/test/number/run.sh b/test/number/run.sh
index 0c5e0cf..7ba4a4b 100755
--- a/test/number/run.sh
+++ b/test/number/run.sh
@@ -1,7 +1,6 @@
 #!/bin/bash
-py=$(which python3 || which python)
-$py gen.py 4 b 2 01xz > binary.sv
-$py gen.py 2 o 8 01234567xz > octal.sv
-$py gen.py 2 d 10 0123456789 > decimal.sv
-$py gen.py 2 h 16 0123456789abcdefxz > hex.sv
+python3 gen.py 4 b 2 01xz > binary.sv
+python3 gen.py 2 o 8 01234567xz > octal.sv
+python3 gen.py 2 d 10 0123456789 > decimal.sv
+python3 gen.py 2 h 16 0123456789abcdefxz > hex.sv
 source ../lib/runner.sh