diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index d3b2028..343283b 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -21,6 +21,7 @@ jobs:
           wget https://apt.llvm.org/llvm.sh
           chmod +x llvm.sh
           sudo ./llvm.sh $LLVM_VERSION
+          sudo apt update -y && sudo apt upgrade -y
           sudo apt-get -y install gcc-multilib g++-multilib clang-tidy-$LLVM_VERSION
           sudo update-alternatives --install /usr/bin/clang-tidy clang-tidy /usr/bin/clang-tidy-$LLVM_VERSION 50
           clang-tidy --version
@@ -57,7 +58,9 @@ jobs:
             cxx-compiler: clang++
     steps:
       - uses: actions/checkout@v2
-      - run: sudo apt install gcc-multilib g++-multilib
+      - run: |
+          sudo apt update -y && sudo apt upgrade -y
+          sudo apt install gcc-multilib g++-multilib
       - run: >
           cmake
           -B ${{ github.workspace }}/build
@@ -85,6 +88,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - run: |
+          sudo apt update -y && sudo apt upgrade -y
           sudo apt install gcc-avr avr-libc
           avr-gcc --version
       - run: avr-gcc libcanard/*.c -c -std=c99 -mmcu=${{ env.mcu }} ${{ env.flags }}
@@ -117,7 +121,9 @@ jobs:
         fetch-depth: 0
 
     - name: Install Dependencies
-      run: sudo apt install gcc-multilib g++-multilib
+      run: |
+        sudo apt update -y && sudo apt upgrade -y
+        sudo apt install -y gcc-multilib g++-multilib
 
     - name: Set up JDK
       uses: actions/setup-java@v1
diff --git a/libcanard/canard.c b/libcanard/canard.c
index 685e8fc..e2ab4ae 100644
--- a/libcanard/canard.c
+++ b/libcanard/canard.c
@@ -151,12 +151,7 @@ CANARD_PRIVATE TransferCRC crcAdd(const TransferCRC crc, const size_t size, cons
 typedef struct TxItem
 {
     CanardTxQueueItem base;
-
-    // Intentional violation of MISRA: this flex array is the lesser of three evils. The other two are:
-    //  - Make the payload pointer point to the remainder of the allocated memory following this structure.
-    //    The pointer is bad because it requires us to use pointer arithmetics.
-    //  - Use a separate memory allocation for data. This is terribly wasteful (both time & memory).
-    uint8_t payload_buffer[];  // NOSONAR
+    uint8_t           payload_buffer[CANARD_MTU_MAX];
 } TxItem;
 
 /// Chain of TX frames prepared for insertion into a TX queue.
@@ -304,7 +299,7 @@ CANARD_PRIVATE TxItem* txAllocateQueueItem(CanardInstance* const   ins,
 {
     CANARD_ASSERT(ins != NULL);
     CANARD_ASSERT(payload_size > 0U);
-    TxItem* const out = (TxItem*) ins->memory_allocate(ins, sizeof(TxItem) + payload_size);
+    TxItem* const out = (TxItem*) ins->memory_allocate(ins, sizeof(TxItem) - CANARD_MTU_MAX + payload_size);
     if (out != NULL)
     {
         out->base.base.up    = NULL;
diff --git a/libcanard/canard.h b/libcanard/canard.h
index c2737a8..47f06f4 100644
--- a/libcanard/canard.h
+++ b/libcanard/canard.h
@@ -114,6 +114,7 @@ extern "C" {
 /// Per the recommendations given in the UAVCAN/CAN Specification, other MTU values should not be used.
 #define CANARD_MTU_CAN_CLASSIC 8U
 #define CANARD_MTU_CAN_FD 64U
+#define CANARD_MTU_MAX CANARD_MTU_CAN_FD
 
 /// Parameter ranges are inclusive; the lower bound is zero for all. See UAVCAN/CAN Specification for background.
 #define CANARD_SUBJECT_ID_MAX 8191U
diff --git a/tools/Dockerfile b/tools/Dockerfile
index 3f71063..769145a 100644
--- a/tools/Dockerfile
+++ b/tools/Dockerfile
@@ -11,10 +11,13 @@ ENV DEBIAN_FRONTEND noninteractive
 RUN apt-get update && apt-get -y upgrade
 RUN apt-get -y --no-install-recommends install \
 		build-essential cmake gcc-multilib g++-multilib \
-		clang-tidy-13 clang-format-13 \
+		clang-tidy-12 clang-format-12 \
 		gcc-avr avr-libc \
 		sudo curl git ca-certificates
 
+RUN update-alternatives --install /usr/bin/clang-tidy clang-tidy /usr/bin/clang-tidy-12 10
+RUN update-alternatives --install /usr/bin/clang-format clang-format /usr/bin/clang-format-12 10
+
 # borrowed from MAVSDK https://github.com/mavlink/MAVSDK/blob/main/docker/Dockerfile-Ubuntu-20.04
 RUN curl -L https://github.com/ncopa/su-exec/archive/dddd1567b7c76365e1e0aac561287975020a8fad.tar.gz | tar xvz && \
 	cd su-exec-* && make && mv su-exec /usr/local/bin && cd .. && rm -rf su-exec-*