diff --git a/src/frontend/get_avail_mem_size.c b/src/frontend/get_avail_mem_size.c
index c40702baa..3d468b659 100644
--- a/src/frontend/get_avail_mem_size.c
+++ b/src/frontend/get_avail_mem_size.c
@@ -9,7 +9,7 @@
 
 #if defined(_WIN32)
 #undef BOOLEAN
-#include <Windows.h>
+#include <windows.h>
 
 #elif defined(__unix__) || defined(__unix) || defined(unix) || (defined(__APPLE__) && defined(__MACH__))
 #include <unistd.h>
diff --git a/src/frontend/get_phys_mem_size.c b/src/frontend/get_phys_mem_size.c
index 378f7115d..3ebb92407 100644
--- a/src/frontend/get_phys_mem_size.c
+++ b/src/frontend/get_phys_mem_size.c
@@ -11,7 +11,7 @@
 
 #if defined(_WIN32)
 #undef BOOLEAN
-#include <Windows.h>
+#include <windows.h>
 
 #elif defined(__unix__) || defined(__unix) || defined(unix) || (defined(__APPLE__) && defined(__MACH__))
 #include <unistd.h>
diff --git a/src/xspice/cmpp/main.c b/src/xspice/cmpp/main.c
index 98d80e764..139d18612 100644
--- a/src/xspice/cmpp/main.c
+++ b/src/xspice/cmpp/main.c
@@ -37,7 +37,7 @@ NON-STANDARD FEATURES
 ============================================================================*/
 #ifdef DEBUG_CMPP
 #ifdef _WIN32
-#include <Windows.h>
+#include <windows.h>
 #endif
 #endif