diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5c5da58f..c9a3b49e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -16,7 +16,7 @@ env:
   AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
   AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
   AWS_REGION: us-east-1
-  
+
 jobs:
   linux-compat:
     runs-on: ubuntu-latest
@@ -36,7 +36,7 @@ jobs:
     - name: Build ${{ env.PACKAGE_NAME }}
       run: |
         aws s3 cp s3://aws-crt-test-stuff/ci/${{ env.BUILDER_VERSION }}/linux-container-ci.sh ./linux-container-ci.sh && chmod a+x ./linux-container-ci.sh
-        ./linux-container-ci.sh ${{ env.BUILDER_VERSION }} aws-crt-${{ matrix.image }} build -p ${{ env.PACKAGE_NAME }} downstream
+        ./linux-container-ci.sh ${{ env.BUILDER_VERSION }} aws-crt-${{ matrix.image }} build -p ${{ env.PACKAGE_NAME }} --cmake-extra=-DASSERT_LOCK_HELD=ON downstream
 
   linux-compiler-compat:
     runs-on: ubuntu-latest
@@ -59,7 +59,7 @@ jobs:
       - name: Build ${{ env.PACKAGE_NAME }}
         run: |
           aws s3 cp s3://aws-crt-test-stuff/ci/${{ env.BUILDER_VERSION }}/linux-container-ci.sh ./linux-container-ci.sh && chmod a+x ./linux-container-ci.sh
-          ./linux-container-ci.sh ${{ env.BUILDER_VERSION }} aws-crt-${{ env.LINUX_BASE_IMAGE }} build -p ${{ env.PACKAGE_NAME }} --compiler=${{ matrix.compiler }} --spec downstream
+          ./linux-container-ci.sh ${{ env.BUILDER_VERSION }} aws-crt-${{ env.LINUX_BASE_IMAGE }} build -p ${{ env.PACKAGE_NAME }} --compiler=${{ matrix.compiler }} --cmake-extra=-DASSERT_LOCK_HELD=ON --spec downstream
 
   clang-sanitizers:
     runs-on: ubuntu-latest
@@ -71,7 +71,7 @@ jobs:
       - name: Build ${{ env.PACKAGE_NAME }}
         run: |
           aws s3 cp s3://aws-crt-test-stuff/ci/${{ env.BUILDER_VERSION }}/linux-container-ci.sh ./linux-container-ci.sh && chmod a+x ./linux-container-ci.sh
-          ./linux-container-ci.sh ${{ env.BUILDER_VERSION }} aws-crt-${{ env.LINUX_BASE_IMAGE }} build -p ${{ env.PACKAGE_NAME }} --compiler=clang-11 --cmake-extra=-DENABLE_SANITIZERS=ON --cmake-extra=-DSANITIZERS="${{ matrix.sanitizers }}"
+          ./linux-container-ci.sh ${{ env.BUILDER_VERSION }} aws-crt-${{ env.LINUX_BASE_IMAGE }} build -p ${{ env.PACKAGE_NAME }} --compiler=clang-11 --cmake-extra=-DENABLE_SANITIZERS=ON --cmake-extra=-DASSERT_LOCK_HELD=ON --cmake-extra=-DSANITIZERS="${{ matrix.sanitizers }}"
 
   linux-shared-libs:
     runs-on: ubuntu-latest
@@ -80,7 +80,7 @@ jobs:
       - name: Build ${{ env.PACKAGE_NAME }}
         run: |
           aws s3 cp s3://aws-crt-test-stuff/ci/${{ env.BUILDER_VERSION }}/linux-container-ci.sh ./linux-container-ci.sh && chmod a+x ./linux-container-ci.sh
-          ./linux-container-ci.sh ${{ env.BUILDER_VERSION }} aws-crt-${{ env.LINUX_BASE_IMAGE }} build -p ${{ env.PACKAGE_NAME }} --cmake-extra=-DBUILD_SHARED_LIBS=ON
+          ./linux-container-ci.sh ${{ env.BUILDER_VERSION }} aws-crt-${{ env.LINUX_BASE_IMAGE }} build -p ${{ env.PACKAGE_NAME }} --cmake-extra=-DBUILD_SHARED_LIBS=ON --cmake-extra=-DASSERT_LOCK_HELD=ON
 
   windows:
     runs-on: windows-latest
@@ -88,7 +88,7 @@ jobs:
     - name: Build ${{ env.PACKAGE_NAME }} + consumers
       run: |
         python -c "from urllib.request import urlretrieve; urlretrieve('${{ env.BUILDER_HOST }}/${{ env.BUILDER_SOURCE }}/${{ env.BUILDER_VERSION }}/builder.pyz?run=${{ env.RUN }}', 'builder.pyz')"
-        python builder.pyz build -p ${{ env.PACKAGE_NAME }}
+        python builder.pyz build -p ${{ env.PACKAGE_NAME }} --cmake-extra=-DASSERT_LOCK_HELD=ON
 
   windows-vc14:
     runs-on: windows-latest
@@ -99,7 +99,7 @@ jobs:
     - name: Build ${{ env.PACKAGE_NAME }} + consumers
       run: |
         python -c "from urllib.request import urlretrieve; urlretrieve('${{ env.BUILDER_HOST }}/${{ env.BUILDER_SOURCE }}/${{ env.BUILDER_VERSION }}/builder.pyz?run=${{ env.RUN }}', 'builder.pyz')"
-        python builder.pyz build -p ${{ env.PACKAGE_NAME }} --target windows-${{ matrix.arch }} --compiler msvc-14
+        python builder.pyz build -p ${{ env.PACKAGE_NAME }} --target windows-${{ matrix.arch }} --compiler msvc-14 --cmake-extra=-DASSERT_LOCK_HELD=ON
 
   windows-shared-libs:
     runs-on: windows-latest
@@ -107,7 +107,7 @@ jobs:
     - name: Build ${{ env.PACKAGE_NAME }} + consumers
       run: |
         python -c "from urllib.request import urlretrieve; urlretrieve('${{ env.BUILDER_HOST }}/${{ env.BUILDER_SOURCE }}/${{ env.BUILDER_VERSION }}/builder.pyz?run=${{ env.RUN }}', 'builder.pyz')"
-        python builder.pyz build -p ${{ env.PACKAGE_NAME }} --cmake-extra=-DBUILD_SHARED_LIBS=ON
+        python builder.pyz build -p ${{ env.PACKAGE_NAME }} --cmake-extra=-DBUILD_SHARED_LIBS=ON --cmake-extra=-DASSERT_LOCK_HELD=ON
 
   osx:
     runs-on: macos-latest
@@ -116,6 +116,4 @@ jobs:
       run: |
         python3 -c "from urllib.request import urlretrieve; urlretrieve('${{ env.BUILDER_HOST }}/${{ env.BUILDER_SOURCE }}/${{ env.BUILDER_VERSION }}/builder.pyz?run=${{ env.RUN }}', 'builder')"
         chmod a+x builder
-        ./builder build -p ${{ env.PACKAGE_NAME }} default-downstream
-
-
+        ./builder build -p ${{ env.PACKAGE_NAME }} --cmake-extra=-DASSERT_LOCK_HELD=ON default-downstream
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3d80abb1..45eab337 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -7,6 +7,11 @@ if (POLICY CMP0069)
     cmake_policy(SET CMP0069 NEW) # Enable LTO/IPO if available in the compiler, see AwsCFlags
 endif()
 
+option(ASSERT_LOCK_HELD "Enable ASSERT_SYNCED_DATA_LOCK_HELD for checking thread issue" OFF)
+if (ASSERT_LOCK_HELD)
+    add_definitions(-DASSERT_LOCK_HELD)
+endif()
+
 if (DEFINED CMAKE_PREFIX_PATH)
     file(TO_CMAKE_PATH "${CMAKE_PREFIX_PATH}" CMAKE_PREFIX_PATH)
 endif()
diff --git a/include/aws/mqtt/private/client_impl.h b/include/aws/mqtt/private/client_impl.h
index 387f39aa..f7b4be01 100644
--- a/include/aws/mqtt/private/client_impl.h
+++ b/include/aws/mqtt/private/client_impl.h
@@ -34,7 +34,7 @@
         }                                                                                                              \
     } while (false)
 
-#if DEBUG_BUILD
+#if ASSERT_LOCK_HELD
 #    define ASSERT_SYNCED_DATA_LOCK_HELD(object)                                                                       \
         {                                                                                                              \
             int cached_error = aws_last_error();                                                                       \