diff --git a/.github/workflows/CICD.yml b/.github/workflows/CICD.yml
index 74f1d8ce085..d2cf890a2ee 100644
--- a/.github/workflows/CICD.yml
+++ b/.github/workflows/CICD.yml
@@ -67,7 +67,7 @@ jobs:
     - name: Install `rust` toolchain
       uses: actions-rs/toolchain@v1
       with:
-        toolchain: nightly
+        toolchain: nightly-2022-03-21
         default: true
         profile: minimal
     - name: Install `cargo-udeps`
@@ -86,7 +86,7 @@ jobs:
         fault_type="${{ steps.vars.outputs.FAULT_TYPE }}"
         fault_prefix=$(echo "$fault_type" | tr '[:lower:]' '[:upper:]')
         #
-        cargo +nightly udeps ${{ steps.vars.outputs.CARGO_FEATURES_OPTION }} --all-targets &> udeps.log || cat udeps.log
+        cargo +nightly-2022-03-21 udeps ${{ steps.vars.outputs.CARGO_FEATURES_OPTION }} --all-targets &> udeps.log || cat udeps.log
         grep --ignore-case "all deps seem to have been used" udeps.log || { printf "%s\n" "::${fault_type} ::${fault_prefix}: \`cargo udeps\`: style violation (unused dependency found)" ; fault=true ; }
         if [ -n "${{ steps.vars.outputs.FAIL_ON_FAULT }}" ] && [ -n "$fault" ]; then exit 1 ; fi
 
@@ -483,7 +483,7 @@ jobs:
     - name: Install `rust` toolchain
       uses: actions-rs/toolchain@v1
       with:
-        toolchain: nightly
+        toolchain: nightly-2022-03-21
         default: true
         profile: minimal # minimal component installation (ie, no documentation)
     - name: Test
@@ -919,7 +919,6 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        # job: [ { os: ubuntu-latest }, { os: macos-latest }, { os: windows-latest } ]
         job:
           - { os: ubuntu-latest  , features: unix }
           - { os: macos-latest   , features: macos }
@@ -936,7 +935,7 @@ jobs:
         ## VARs setup
         outputs() { step_id="vars"; for var in "$@" ; do echo steps.${step_id}.outputs.${var}="${!var}"; echo ::set-output name=${var}::${!var}; done; }
         # toolchain
-        TOOLCHAIN="nightly" ## default to "nightly" toolchain (required for certain required unstable compiler flags) ## !maint: refactor when stable channel has needed support
+        TOOLCHAIN="nightly-2022-03-21" ## default to "nightly" toolchain (required for certain required unstable compiler flags) ## !maint: refactor when stable channel has needed support
         # * specify gnu-type TOOLCHAIN for windows; `grcov` requires gnu-style code coverage data files
         case ${{ matrix.job.os }} in windows-*) TOOLCHAIN="$TOOLCHAIN-x86_64-pc-windows-gnu" ;; esac;
         # * use requested TOOLCHAIN if specified
diff --git a/.github/workflows/GnuTests.yml b/.github/workflows/GnuTests.yml
index 1f24f304584..fbd6f4c0fc7 100644
--- a/.github/workflows/GnuTests.yml
+++ b/.github/workflows/GnuTests.yml
@@ -218,7 +218,7 @@ jobs:
     - name: Install `rust` toolchain
       uses: actions-rs/toolchain@v1
       with:
-        toolchain: nightly
+        toolchain: nightly-2022-03-21
         default: true
         profile: minimal # minimal component installation (ie, no documentation)
         components: rustfmt