diff --git a/CMakeLists.txt b/CMakeLists.txt
index 210cc38f34..0cb208e988 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -177,6 +177,9 @@ string(REGEX MATCH "Clang" CMAKE_COMPILER_IS_CLANG "${CMAKE_C_COMPILER_ID}")
 
 include(CheckCCompilerFlag)
 
+set(CMAKE_C_EXTENSIONS OFF)
+set(CMAKE_C_STANDARD 99)
+
 if(CMAKE_COMPILER_IS_GNU)
     # some warnings we want are not available with old GCC versions
     # note: starting with CMake 2.8 we could use CMAKE_C_COMPILER_VERSION
@@ -294,6 +297,8 @@ if(ENABLE_TESTING OR ENABLE_PROGRAMS)
         PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/tests/include
         PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/include
         PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/library)
+    # Request C11, needed for memory poisoning tests
+    set_target_properties(mbedtls_test PROPERTIES C_STANDARD 11)
 
     file(GLOB MBEDTLS_TEST_HELPER_FILES
          ${CMAKE_CURRENT_SOURCE_DIR}/tests/src/test_helpers/*.c)
diff --git a/programs/test/CMakeLists.txt b/programs/test/CMakeLists.txt
index 0778731125..5a26821b51 100644
--- a/programs/test/CMakeLists.txt
+++ b/programs/test/CMakeLists.txt
@@ -78,6 +78,9 @@ foreach(exe IN LISTS executables_libs executables_mbedcrypto)
         target_include_directories(${exe} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
     endif()
 
+    # Request C11, required for memory poisoning
+    set_target_properties(${exe} PROPERTIES C_STANDARD 11)
+
     # This emulates "if ( ... IN_LIST ... )" which becomes available in CMake 3.3
     list(FIND executables_libs ${exe} exe_index)
     if (${exe_index} GREATER -1)
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 0869aaa018..188d5d595f 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -251,6 +251,8 @@ function(add_test_suite suite_name)
     target_include_directories(test_suite_${data_name}
         PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/include
         PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/../library)
+    # Request C11, which is needed for memory poisoning tests
+    set_target_properties(test_suite_${data_name} PROPERTIES C_STANDARD 11)
 
     if(${data_name} MATCHES ${SKIP_TEST_SUITES_REGEX})
         message(STATUS "The test suite ${data_name} will not be executed.")