diff --git a/ci/azure/linux_script b/ci/azure/linux_script
index b313a7616..a55de2449 100755
--- a/ci/azure/linux_script
+++ b/ci/azure/linux_script
@@ -12,7 +12,7 @@ sudo apt-get update -q
 
 sudo apt-get remove -y llvm-*
 sudo rm -rf /usr/local/*
-sudo apt-get install -y libxml2-dev libclang-10-dev llvm-10 llvm-10-dev liblld-10-dev cmake s3cmd gcc-7 g++-7 ninja-build
+sudo apt-get install -y libxml2-dev libclang-10-dev llvm-10 llvm-10-dev liblld-10-dev cmake s3cmd gcc-7 g++-7 ninja-build tidy
 
 QEMUBASE="qemu-linux-x86_64-5.0.0-49ee115552"
 wget https://ziglang.org/deps/$QEMUBASE.tar.xz
@@ -51,6 +51,10 @@ cd build
 cmake .. -DCMAKE_BUILD_TYPE=Release -GNinja
 ninja install
 ./zig build test -Denable-qemu -Denable-wasmtime
+
+# look for HTML errors
+tidy -qe ../zig-cache/langref.html
+
 VERSION="$(./zig version)"
 
 if [ "${BUILD_REASON}" != "PullRequest" ]; then
diff --git a/doc/langref.html.in b/doc/langref.html.in
index 032e05d60..78dcd537b 100644
--- a/doc/langref.html.in
+++ b/doc/langref.html.in
@@ -8419,6 +8419,7 @@ fn foo(comptime T: type, ptr: *T) T {
       {#header_close#}
 
       {#header_open|Opaque Types#}
+      <p>
       {#syntax#}@Type(.Opaque){#endsyntax#} creates a new type with an unknown (but non-zero) size and alignment.
       </p>
       <p>