diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 70aebfc87..afe61ddab 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -13,7 +13,7 @@ jobs:
       run: make BUILD_TLS=yes
     - name: test
       run: |
-        sudo apt-get install tcl8.5
+        sudo apt-get install tcl8.6
         ./runtest --verbose
     - name: module api test
       run: ./runtest-moduleapi --verbose
diff --git a/.github/workflows/daily.yml b/.github/workflows/daily.yml
index 61e3dee1f..c75d1d00c 100644
--- a/.github/workflows/daily.yml
+++ b/.github/workflows/daily.yml
@@ -20,7 +20,7 @@ jobs:
       run: make
     - name: test
       run: |
-        sudo apt-get install tcl8.5
+        sudo apt-get install tcl8.6
         ./runtest --accurate --verbose
     - name: module api test
       run: ./runtest-moduleapi --verbose
@@ -39,7 +39,7 @@ jobs:
       run: make MALLOC=libc
     - name: test
       run: |
-        sudo apt-get install tcl8.5
+        sudo apt-get install tcl8.6
         ./runtest --accurate --verbose
     - name: module api test
       run: ./runtest-moduleapi --verbose
@@ -60,7 +60,7 @@ jobs:
         make 32bit
     - name: test
       run: |
-        sudo apt-get install tcl8.5
+        sudo apt-get install tcl8.6
         ./runtest --accurate --verbose
     - name: module api test
       run: |
@@ -82,7 +82,7 @@ jobs:
         make BUILD_TLS=yes
     - name: test
       run: |
-        sudo apt-get install tcl8.5 tcl-tls
+        sudo apt-get install tcl8.6 tcl-tls
         ./utils/gen-test-certs.sh
         ./runtest --accurate --verbose --tls
         ./runtest --accurate --verbose
@@ -110,7 +110,7 @@ jobs:
     - name: test
       run: |
         sudo apt-get update
-        sudo apt-get install tcl8.5 valgrind -y
+        sudo apt-get install tcl8.6 valgrind -y
         ./runtest --valgrind --verbose --clients 1
     - name: module api test
       run: ./runtest-moduleapi --valgrind --verbose --clients 1