diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3f76da187..804b01b08 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -9,6 +9,7 @@ on:
 env:
   RUST_BACKTRACE: 1
   RUSTFLAGS: -Dwarnings
+  RUST_NIGHTLY: nightly-2024-02-03
 
 
 jobs:
@@ -18,7 +19,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macOS-latest]
-        rust: [nightly, beta, stable]
+        rust: [$RUST_NIGHTLY, beta, stable]
 
     steps:
     - name: Checkout
@@ -40,7 +41,7 @@ jobs:
 
     - name: check nightly
       uses: actions-rs/cargo@v1
-      if: matrix.rust == 'nightly'
+      if: matrix.rust == '$RUST_NIGHTLY'
       with:
         command:  check
         args: --features nightly --all --bins --examples --tests
@@ -55,14 +56,14 @@ jobs:
 
     - name: check bench
       uses: actions-rs/cargo@v1
-      if: matrix.rust == 'nightly'
+      if: matrix.rust == '$RUST_NIGHTLY'
       with:
         command:  check
         args: --benches
 
     - name: check asm
       uses: actions-rs/cargo@v1
-      if: matrix.rust == 'nightly'
+      if: matrix.rust == '$RUST_NIGHTLY'
       with:
         command:  check
         args: --features asm
@@ -75,14 +76,14 @@ jobs:
 
     - name: nightly
       uses: actions-rs/cargo@v1
-      if: matrix.rust == 'nightly'
+      if: matrix.rust == '$RUST_NIGHTLY'
       with:
         command: test
         args: --all  --features nightly
 
     - name: asm
       uses: actions-rs/cargo@v1
-      if: matrix.rust == 'nightly'
+      if: matrix.rust == '$RUST_NIGHTLY'
       with:
         command: test
         args: --all --features asm
@@ -95,14 +96,14 @@ jobs:
 
     - name: nightly ignored
       uses: actions-rs/cargo@v1
-      if: matrix.rust == 'nightly'
+      if: matrix.rust == '$RUST_NIGHTLY'
       with:
         command: test
         args: --all --features nightly --release -- --ignored
 
     - name: asm ignored
       uses: actions-rs/cargo@v1
-      if: matrix.rust == 'nightly'
+      if: matrix.rust == '$RUST_NIGHTLY'
       with:
         command: test
         args: --all --features asm --release -- --ignored
@@ -114,7 +115,7 @@ jobs:
     strategy:
       matrix:
         os: [windows-latest]
-        rust: [nightly, beta, stable]
+        rust: [$RUST_NIGHTLY, beta, stable]
         target:
           - x86_64-pc-windows-gnu
           # FIXME
@@ -142,7 +143,7 @@ jobs:
 
     - name: check nightly
       uses: actions-rs/cargo@v1
-      if: matrix.rust == 'nightly'
+      if: matrix.rust == '$RUST_NIGHTLY'
       with:
         command:  check
         args: --features nightly --all --bins --examples --tests --target ${{ matrix.target }}
@@ -156,7 +157,7 @@ jobs:
 
     - name: check bench
       uses: actions-rs/cargo@v1
-      if: matrix.rust == 'nightly'
+      if: matrix.rust == '$RUST_NIGHTLY'
       with:
         command:  check
         target: ${{ matrix.target }}
@@ -164,7 +165,7 @@ jobs:
 
     - name: check asm
       uses: actions-rs/cargo@v1
-      if: matrix.rust == 'nightly' && matrix.target == 'x86_64-pc-windows-gnu'
+      if: matrix.rust == '$RUST_NIGHTLY' && matrix.target == 'x86_64-pc-windows-gnu'
       with:
         command:  check
         args: --features asm  --target ${{ matrix.target }}
@@ -177,7 +178,7 @@ jobs:
 
     - name: nightly
       uses: actions-rs/cargo@v1
-      if: matrix.rust == 'nightly'
+      if: matrix.rust == '$RUST_NIGHTLY'
       with:
         command: test
         args: --all  --features nightly --target ${{ matrix.target }}
@@ -185,7 +186,7 @@ jobs:
     # FIXME
     # - name: asm
     #   uses: actions-rs/cargo@v1
-    #   if: matrix.rust == 'nightly' && matrix.target == 'x86_64-pc-windows-gnu'
+    #   if: matrix.rust == '$RUST_NIGHTLY' && matrix.target == 'x86_64-pc-windows-gnu'
     #   with:
     #     command: test
     #     args: --all  --features asm --target ${{ matrix.target }}
@@ -198,7 +199,7 @@ jobs:
 
     - name: nightly ignored
       uses: actions-rs/cargo@v1
-      if: matrix.rust == 'nightly'
+      if: matrix.rust == '$RUST_NIGHTLY'
       with:
         command: test
         args: --all  --features nightly --target ${{ matrix.target }} --release -- --ignored
@@ -206,7 +207,7 @@ jobs:
     # FIXME
     # - name: asm ignored
     #   uses: actions-rs/cargo@v1
-    #   if: matrix.rust == 'nightly' && matrix.target == 'x86_64-pc-windows-gnu'
+    #   if: matrix.rust == '$RUST_NIGHTLY' && matrix.target == 'x86_64-pc-windows-gnu'
     #   with:
     #     command: test
     #     args: --all  --features asm --target ${{ matrix.target }} --release -- --ignored
@@ -249,7 +250,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        rust: [nightly, beta, stable]
+        rust: [$RUST_NIGHTLY, beta, stable]
 
     steps:
     - uses: actions/checkout@master
@@ -282,7 +283,7 @@ jobs:
     - uses: actions-rs/toolchain@v1
       with:
           profile: minimal
-          toolchain: nightly
+          toolchain: $RUST_NIGHTLY
           override: true
           components: rustfmt
 
@@ -304,7 +305,7 @@ jobs:
     - uses: actions-rs/toolchain@v1
       with:
           profile: minimal
-          toolchain: nightly
+          toolchain: $RUST_NIGHTLY
           override: true
           components: clippy
     - uses: actions-rs/clippy-check@v1