diff --git .github/workflows/linux-build.yml .github/workflows/linux-build.yml
index a17751ce1d..47d5ebffb9 100644
--- .github/workflows/linux-build.yml
+++ .github/workflows/linux-build.yml
@@ -16,7 +16,7 @@ jobs:
       matrix:
         cfgopt:
           - ""
-          - "CFLAGS=-DTCL_NO_DEPRECATED=1"
+          - "CPPFLAGS=-DTCL_NO_DEPRECATED=1"
           - "--disable-shared"
           - "--enable-symbols"
           - "--enable-symbols=mem"
diff --git .github/workflows/win-build.yml .github/workflows/win-build.yml
index 2b772f91af..8517fdf431 100644
--- .github/workflows/win-build.yml
+++ .github/workflows/win-build.yml
@@ -60,7 +60,7 @@ jobs:
       matrix:
         cfgopt:
           - ""
-          - "CFLAGS=-DTCL_NO_DEPRECATED=1"
+          - "CPPFLAGS=-DTCL_NO_DEPRECATED=1"
           - "--disable-shared"
           - "--enable-symbols"
           - "--enable-symbols=mem"
diff --git .travis.yml .travis.yml
index b63be12e99..d7876f838a 100644
--- .travis.yml
+++ .travis.yml
@@ -26,7 +26,7 @@ jobs:
       compiler: gcc
       env:
         - BUILD_DIR=unix
-        - CFGOPT="CFLAGS=-DTCL_NO_DEPRECATED=1"
+        - CFGOPT="CPPFLAGS=-DTCL_NO_DEPRECATED=1"
     - name: "Linux/GCC/Static"
       os: linux
       dist: focal
@@ -82,7 +82,7 @@ jobs:
       compiler: clang
       env:
         - BUILD_DIR=unix
-        - CFGOPT="CFLAGS=-DTCL_NO_DEPRECATED=1"
+        - CFGOPT="CPPFLAGS=-DTCL_NO_DEPRECATED=1"
     - name: "Linux/Clang/Static"
       os: linux
       dist: focal
@@ -306,7 +306,7 @@ jobs:
       compiler: gcc
       env:
         - BUILD_DIR=win
-        - CFGOPT="--enable-64bit CFLAGS=-DTCL_NO_DEPRECATED=1"
+        - CFGOPT="--enable-64bit CPPFLAGS=-DTCL_NO_DEPRECATED=1"
       before_install: *makepreinst
     - name: "Windows/GCC/Static"
       os: windows
@@ -341,7 +341,7 @@ jobs:
       compiler: gcc
       env:
         - BUILD_DIR=win
-        - CFGOPT="CFLAGS=-DTCL_NO_DEPRECATED=1"
+        - CFGOPT="CPPFLAGS=-DTCL_NO_DEPRECATED=1"
       before_install: *makepreinst
     - name: "Windows/GCC-x86/Static"
       os: windows
