diff --git a/Modules/CheckIncludeFiles.cmake b/Modules/CheckIncludeFiles.cmake
index 8e82859877..8fc6921ca2 100644
--- a/Modules/CheckIncludeFiles.cmake
+++ b/Modules/CheckIncludeFiles.cmake
@@ -70,10 +70,11 @@ macro(CHECK_INCLUDE_FILES INCLUDE VARIABLE)
       message(FATAL_ERROR "Unknown arguments:\n  ${ARGN}\n")
     endif()
 
+    string(MAKE_C_IDENTIFIER ${VARIABLE} _variable_escaped)
     if(_lang STREQUAL "C")
-      set(src ${VARIABLE}.c)
+      set(src ${_variable_escaped}.c)
     elseif(_lang STREQUAL "CXX")
-      set(src ${VARIABLE}.cpp)
+      set(src ${_variable_escaped}.cpp)
     else()
       message(FATAL_ERROR "Unknown language:\n  ${_lang}\nSupported languages: C, CXX.\n")
     endif()
diff --git a/Modules/CheckTypeSize.cmake b/Modules/CheckTypeSize.cmake
index b14ab06920..e09b7c8489 100644
--- a/Modules/CheckTypeSize.cmake
+++ b/Modules/CheckTypeSize.cmake
@@ -103,10 +103,11 @@ function(__check_type_size_impl type var map builtin language)
   endif()
 
   # Perform language check
+  string(MAKE_C_IDENTIFIER ${var} _var_escaped)
   if(language STREQUAL "C")
-    set(src ${var}.c)
+    set(src ${_var_escaped}.c)
   elseif(language STREQUAL "CXX")
-    set(src ${var}.cpp)
+    set(src ${_var_escaped}.cpp)
   else()
     message(FATAL_ERROR "Unknown language:\n  ${language}\nSupported languages: C, CXX.\n")
   endif()