diff --git a/local/recipes/kde/kf6-ki18n/recipe.toml b/local/recipes/kde/kf6-ki18n/recipe.toml
index 2659c817b3..1bff4d432a 100644
--- a/local/recipes/kde/kf6-ki18n/recipe.toml
+++ b/local/recipes/kde/kf6-ki18n/recipe.toml
@@ -40,6 +40,8 @@ cmake "${COOKBOOK_SOURCE}" \
     -DCMAKE_INSTALL_PREFIX=/usr \
     -DCMAKE_BUILD_TYPE=Release \
     -DCMAKE_PREFIX_PATH="${COOKBOOK_SYSROOT}" \
+    -DCMAKE_C_FLAGS="-U_GLIBCXX_USE_C99_STDLIB" \
+    -DCMAKE_CXX_FLAGS="-U_GLIBCXX_USE_C99_STDLIB" \
     -DCMAKE_C_STANDARD_LIBRARIES="-liconv" \
     -DCMAKE_CXX_STANDARD_LIBRARIES="-liconv" \
     -DCMAKE_SHARED_LINKER_FLAGS="-liconv" \
diff --git a/local/recipes/qt/redox-toolchain.cmake b/local/recipes/qt/redox-toolchain.cmake
index 8bff6fca8d..fa19e0c8be 100644
--- a/local/recipes/qt/redox-toolchain.cmake
+++ b/local/recipes/qt/redox-toolchain.cmake
@@ -42,10 +42,10 @@ set(CMAKE_SYSTEM_VERSION 1)
 
 # Redox userspace currently must not emit CET/IBT entry instructions (endbr64),
 # because they trap as invalid opcode in the current runtime stack.
-set(CMAKE_C_FLAGS "-fcf-protection=none -march=x86-64 -include strings.h -include stdlib.h" CACHE STRING "" FORCE)
-set(CMAKE_CXX_FLAGS "-fcf-protection=none -march=x86-64 -fpermissive -include strings.h -include stdlib.h -I${COOKBOOK_SYSROOT}/usr/include/QtQml -I${COOKBOOK_SYSROOT}/usr/include/QtQuick" CACHE STRING "" FORCE)
-set(CMAKE_C_FLAGS_RELEASE "-fcf-protection=none -march=x86-64 -include strings.h -include stdlib.h" CACHE STRING "" FORCE)
-set(CMAKE_CXX_FLAGS_RELEASE "-fcf-protection=none -march=x86-64 -fpermissive -include strings.h -include stdlib.h" CACHE STRING "" FORCE)
+set(CMAKE_C_FLAGS "-fcf-protection=none -march=x86-64 -include strings.h -include stdlib.h -U_GLIBCXX_USE_C99_STDLIB" CACHE STRING "" FORCE)
+set(CMAKE_CXX_FLAGS "-fcf-protection=none -march=x86-64 -fpermissive -include strings.h -include stdlib.h -U_GLIBCXX_USE_C99_STDLIB -I${COOKBOOK_SYSROOT}/usr/include/QtQml -I${COOKBOOK_SYSROOT}/usr/include/QtQuick" CACHE STRING "" FORCE)
+set(CMAKE_C_FLAGS_RELEASE "-fcf-protection=none -march=x86-64 -include strings.h -include stdlib.h -U_GLIBCXX_USE_C99_STDLIB" CACHE STRING "" FORCE)
+set(CMAKE_CXX_FLAGS_RELEASE "-fcf-protection=none -march=x86-64 -fpermissive -include strings.h -include stdlib.h -U_GLIBCXX_USE_C99_STDLIB" CACHE STRING "" FORCE)
 
 # Flag for redox.patch: enables REDOX-specific CMake code paths (mkspec, QPA plugin).
 # QtPlatformSupport.cmake checks this variable. Set as CACHE INTERNAL so it persists