diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 5560158262..1bc597c9c2 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -52,6 +52,17 @@ jobs:
         run: ./build --configuration=${{ matrix.configuration}}
       - name: Run tests
         run: xvfb-run ./build test+only --configuration=${{ matrix.configuration }} --where="Category!=FlakyNetwork"
+      - name: Run inflator container smoke test
+        run: |
+          cd _build
+          curl -fsSL https://get.docker.com -o get-docker.sh
+          sh get-docker.sh
+          docker build --tag inflator --file ../Dockerfile.netkan .
+          docker run --rm --name inflator --entrypoint /bin/bash inflator -c "
+            curl -O https://raw.githubusercontent.com/KSP-CKAN/NetKAN/master/NetKAN/ZeroMiniAVC.netkan && \
+            mono netkan.exe ZeroMiniAVC.netkan
+          "
+        if: matrix.configuration == 'release' && ( matrix.mono == '6.8' || matrix.mono == 'latest' )
 
       - name: Upload ckan.exe artifact
         uses: actions/upload-artifact@v2
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 40cca794fc..d76b10e6fc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -30,6 +30,7 @@ All notable changes to this project will be documented in this file.
 - [Netkan] Fill more info from GitHub for SpaceDock mods (#3390 by: HebaruSan; reviewed: DasSkelett)
 - [Spec] YAMLize netkan spec (#3438 by: HebaruSan; reviewed: DasSkelett)
 - [Netkan] Append resource links to staging PRs (#3454 by: HebaruSan; reviewed: techman83)
+- [Infra] Remove expired Let's Encrypt root certificate from Mono containers (#3457 by: DasSkelett; reviewed: HebaruSan)
 
 ## v1.30.4 (Hubble)
 
diff --git a/Dockerfile.metadata b/Dockerfile.metadata
index dcca6df96a..a04026a577 100644
--- a/Dockerfile.metadata
+++ b/Dockerfile.metadata
@@ -1,5 +1,7 @@
 FROM mono:latest
 
+RUN /bin/sed -i 's/^mozilla\/DST_Root_CA_X3.crt$/!mozilla\/DST_Root_CA_X3.crt/' /etc/ca-certificates.conf && \
+    /usr/sbin/update-ca-certificates
 RUN apt-get update && \
     apt-get install -y --no-install-recommends python3 python3-pip python3-setuptools git build-essential python3-dev && \
     apt-get clean
diff --git a/Dockerfile.netkan b/Dockerfile.netkan
index 962b757907..46ccfee6bd 100644
--- a/Dockerfile.netkan
+++ b/Dockerfile.netkan
@@ -1,4 +1,6 @@
 FROM mono:latest
+RUN /bin/sed -i 's/^mozilla\/DST_Root_CA_X3.crt$/!mozilla\/DST_Root_CA_X3.crt/' /etc/ca-certificates.conf && \
+    /usr/sbin/update-ca-certificates
 RUN useradd -ms /bin/bash netkan
 USER netkan
 WORKDIR /home/netkan