diff --git a/openmp/cmake/HandleOpenMPOptions.cmake b/openmp/cmake/HandleOpenMPOptions.cmake
index 3ed046c7481a..eb7b286b3383 100644
--- a/openmp/cmake/HandleOpenMPOptions.cmake
+++ b/openmp/cmake/HandleOpenMPOptions.cmake
@@ -21,6 +21,7 @@ endif()
 # Additional warnings that are not enabled by -Wall.
 append_if(OPENMP_HAVE_WCAST_QUAL_FLAG "-Wcast-qual" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WFORMAT_PEDANTIC_FLAG "-Wformat-pedantic" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+append_if(OPENMP_HAVE_WIMPLICIT_FALLTHROUGH_FLAG "-Wimplicit-fallthrough" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WSIGN_COMPARE_FLAG "-Wsign-compare" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 
 # Warnings that we want to disable because they are too verbose or fragile.
diff --git a/openmp/cmake/config-ix.cmake b/openmp/cmake/config-ix.cmake
index 8858bc653417..ebb2530ae541 100644
--- a/openmp/cmake/config-ix.cmake
+++ b/openmp/cmake/config-ix.cmake
@@ -6,6 +6,7 @@ check_cxx_compiler_flag(-Werror OPENMP_HAVE_WERROR_FLAG)
 # Additional warnings that are not enabled by -Wall.
 check_cxx_compiler_flag(-Wcast-qual OPENMP_HAVE_WCAST_QUAL_FLAG)
 check_cxx_compiler_flag(-Wformat-pedantic OPENMP_HAVE_WFORMAT_PEDANTIC_FLAG)
+check_cxx_compiler_flag(-Wimplicit-fallthrough OPENMP_HAVE_WIMPLICIT_FALLTHROUGH_FLAG)
 check_cxx_compiler_flag(-Wsign-compare OPENMP_HAVE_WSIGN_COMPARE_FLAG)
 
 # Warnings that we want to disable because they are too verbose or fragile.
diff --git a/openmp/runtime/cmake/LibompHandleFlags.cmake b/openmp/runtime/cmake/LibompHandleFlags.cmake
index 89d66f49f36f..6254f45582d1 100644
--- a/openmp/runtime/cmake/LibompHandleFlags.cmake
+++ b/openmp/runtime/cmake/LibompHandleFlags.cmake
@@ -30,7 +30,6 @@ function(libomp_get_cxxflags cxxflags)
   libomp_append(flags_local -Wno-class-memaccess LIBOMP_HAVE_WNO_CLASS_MEMACCESS_FLAG)
   libomp_append(flags_local -Wno-covered-switch-default LIBOMP_HAVE_WNO_COVERED_SWITCH_DEFAULT_FLAG)
   libomp_append(flags_local -Wno-frame-address LIBOMP_HAVE_WNO_FRAME_ADDRESS_FLAG)
-  libomp_append(flags_local -Wno-implicit-fallthrough LIBOMP_HAVE_WNO_IMPLICIT_FALLTHROUGH_FLAG)
   libomp_append(flags_local -Wno-missing-braces LIBOMP_HAVE_WNO_MISSING_BRACES_FLAG)
   libomp_append(flags_local -Wno-strict-aliasing LIBOMP_HAVE_WNO_STRICT_ALIASING_FLAG)
   libomp_append(flags_local -Wstringop-overflow=0 LIBOMP_HAVE_WSTRINGOP_OVERFLOW_FLAG)
diff --git a/openmp/runtime/cmake/config-ix.cmake b/openmp/runtime/cmake/config-ix.cmake
index abc234c04100..f29aa3c5a32d 100644
--- a/openmp/runtime/cmake/config-ix.cmake
+++ b/openmp/runtime/cmake/config-ix.cmake
@@ -51,7 +51,6 @@ check_cxx_compiler_flag(-fno-rtti LIBOMP_HAVE_FNO_RTTI_FLAG)
 check_cxx_compiler_flag(-Wno-class-memaccess LIBOMP_HAVE_WNO_CLASS_MEMACCESS_FLAG)
 check_cxx_compiler_flag(-Wno-covered-switch-default LIBOMP_HAVE_WNO_COVERED_SWITCH_DEFAULT_FLAG)
 check_cxx_compiler_flag(-Wno-frame-address LIBOMP_HAVE_WNO_FRAME_ADDRESS_FLAG)
-check_cxx_compiler_flag(-Wno-implicit-fallthrough LIBOMP_HAVE_WNO_IMPLICIT_FALLTHROUGH_FLAG)
 check_cxx_compiler_flag(-Wno-missing-braces LIBOMP_HAVE_WNO_MISSING_BRACES_FLAG)
 check_cxx_compiler_flag(-Wno-strict-aliasing LIBOMP_HAVE_WNO_STRICT_ALIASING_FLAG)
 check_cxx_compiler_flag(-Wstringop-overflow=0 LIBOMP_HAVE_WSTRINGOP_OVERFLOW_FLAG)
diff --git a/openmp/runtime/src/thirdparty/ittnotify/ittnotify_static.cpp b/openmp/runtime/src/thirdparty/ittnotify/ittnotify_static.cpp
index 78ab62daeb90..c48b3f420bb7 100644
--- a/openmp/runtime/src/thirdparty/ittnotify/ittnotify_static.cpp
+++ b/openmp/runtime/src/thirdparty/ittnotify/ittnotify_static.cpp
@@ -8,6 +8,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "kmp_config.h"
+#include "kmp_os.h"
 #include "ittnotify_config.h"
 
 #if ITT_PLATFORM==ITT_PLATFORM_WIN
@@ -1096,6 +1097,7 @@ ITT_EXTERN_C int _N_(init_ittlib)(const char* lib_name, __itt_group_id init_grou
                         switch (lib_version) {
                         case 0:
                             groups = __itt_group_legacy;
+                            KMP_FALLTHROUGH();
                         case 1:
                             /* Fill all pointers from dynamic library */
                             for (i = 0; _N_(_ittapi_global).api_list_ptr[i].name != NULL; i++)