diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 31fa872..f309043 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1,5 +1,8 @@
 name: CI
 
+env:
+  OSS_CAD_SUITE: '2026-07-24'
+
 on:
   push:
     branches: [main]
@@ -10,11 +13,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7
-      - name: Install Icarus Verilog
-        run: |
-          sudo grep -rlZ packages.microsoft.com /etc/apt/sources.list.d/ 2>/dev/null | sudo xargs -0 -r rm -f
-          sudo apt-get update
-          sudo apt-get install -y iverilog
+      - uses: YosysHQ/setup-oss-cad-suite@v4
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          version: ${{ env.OSS_CAD_SUITE }}
       - name: synchronizer
         run: make MOD=synchronizer
       - name: tick_gen
@@ -27,6 +29,19 @@ jobs:
         run: make MOD=uart
       - name: board demo (seven_seg + debounce + top)
         run: make -C boards/basys3 test
+
+  # The suite bundles a development build of cocotb whose VPI teardown segfaults
+  # after the test passes, so this job takes iverilog and cocotb from apt and pip.
+  # The same RTL is dialect-checked against the pinned suite by the job above.
+  cocotb:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - name: Install Icarus Verilog
+        run: |
+          sudo grep -rlZ packages.microsoft.com /etc/apt/sources.list.d/ 2>/dev/null | sudo xargs -0 -r rm -f
+          sudo apt-get update
+          sudo apt-get install -y iverilog
       - name: Install cocotb
         run: pip install cocotb
       - name: cocotb top-level loopback
@@ -36,10 +51,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7
-      - name: Install OSS CAD Suite (yosys + sby + solvers)
-        uses: YosysHQ/setup-oss-cad-suite@v4
+      - uses: YosysHQ/setup-oss-cad-suite@v4
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
+          version: ${{ env.OSS_CAD_SUITE }}
       - name: uart_rx formal
         run: make formal MOD=uart_rx
       - name: uart_tx formal