diff --git a/.github/workflows/docker-publish.yml b/.github/workflows/docker-publish.yml
index e56584ae2..dd92f2a91 100644
--- a/.github/workflows/docker-publish.yml
+++ b/.github/workflows/docker-publish.yml
@@ -2,8 +2,17 @@
 # Publish map2check-dev Docker image to GitHub Container Registry
 #
 # Triggers:
-#   - Push to develop (Dockerfile.dev changes)
-#   - Manual dispatch (workflow_dispatch)
+#   - Push to develop (Dockerfile.dev changes)  -> build AND push
+#   - Pull request touching Dockerfile.dev      -> build only, no push
+#   - Manual dispatch (workflow_dispatch)       -> build AND push
+#
+# The pull_request trigger is not decoration. Until it existed, Dockerfile.dev
+# was only ever built after a merge, so a recipe that cannot build reached
+# develop and broke the image: the Clam section built with the default cc
+# (GCC 11) instead of clang-16, and GCC rejects a construct in sea-dsa that
+# clang only warns about. Nothing pre-merge could have caught that, because
+# nothing pre-merge compiled the file. It is paths-filtered, so PRs that do not
+# touch the Dockerfile pay nothing.
 #
 # Phase 1.5 — OpenSSF Best Practices Badge
 ############################################################
@@ -14,6 +23,10 @@ on:
     branches: [develop]
     paths:
       - 'Dockerfile.dev'
+  pull_request:
+    branches: [develop, main, master]
+    paths:
+      - 'Dockerfile.dev'
   workflow_dispatch:
 
 env:
@@ -32,7 +45,10 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
+      # Skipped on pull_request: the run does not push, and a PR from a fork
+      # has no packages:write token to log in with anyway.
       - name: Log in to GHCR
+        if: github.event_name != 'pull_request'
         uses: docker/login-action@v3
         with:
           registry: ${{ env.REGISTRY }}
@@ -48,11 +64,13 @@ jobs:
             type=raw,value=latest
             type=sha,prefix=
 
+      # push is false on pull_request: the point there is to prove the recipe
+      # builds, not to publish an image from an unmerged branch over :latest.
       - name: Build and push
         uses: docker/build-push-action@v5
         with:
           context: .
           file: ./Dockerfile.dev
-          push: true
+          push: ${{ github.event_name != 'pull_request' }}
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
diff --git a/Dockerfile.dev b/Dockerfile.dev
index c82691999..911010dc6 100644
--- a/Dockerfile.dev
+++ b/Dockerfile.dev
@@ -157,6 +157,15 @@ RUN apt-get update && apt-get install -y \
 # CLAM_INCLUDE_TESTS=OFF: Clam's own lit suite needs `lit` from pip and adds
 # build time for tests of a dependency, not of Map2Check.
 #
+# The compilers are named explicitly rather than left to the ENV CC/CXX set in
+# section 11: those are declared 88 lines BELOW this RUN, and a Docker ENV only
+# applies to later instructions, so Clam would silently build with the default
+# cc/c++ (GCC 11). That is not a cosmetic difference -- sea-dsa defines
+# seadsa::mkTLIGetter with a redundant namespace qualification inside its own
+# namespace, which clang accepts as -Wextra-qualification but GCC rejects
+# outright, and the image build dies at 34%. Upstream's own docker/clam.Dockerfile
+# passes these same two flags; clang is the toolchain Clam is built against.
+#
 # The crab / extra / build / install sequence is Clam's documented one. Each
 # target downloads and installs a dependency (Crab, then sea-dsa and
 # llvm-seahorn); the cmake re-run between them re-reads the cache so the next
@@ -165,6 +174,8 @@ RUN git clone --depth 1 -b dev16 https://github.com/seahorn/clam.git /tmp/clam &
     cd /tmp/clam && mkdir build && cd build && \
     CLAM_CFG="-DCMAKE_BUILD_TYPE=Release -DCLAM_LLVM_VERSION=16 \
               -DCLAM_INCLUDE_TESTS=OFF \
+              -DCMAKE_C_COMPILER=/usr/bin/clang-16 \
+              -DCMAKE_CXX_COMPILER=/usr/bin/clang++-16 \
               -DLLVM_DIR=/usr/lib/llvm-16/lib/cmake/llvm \
               -DCMAKE_INSTALL_PREFIX=/opt/clam" && \
     cmake .. $CLAM_CFG && \