diff --git a/include/freerdp/api.h b/include/freerdp/api.h
index b29ab11bb..9cc038744 100644
--- a/include/freerdp/api.h
+++ b/include/freerdp/api.h
@@ -52,7 +52,7 @@
 #endif
 #endif
 #else
-#if __GNUC__ >= 4
+#if defined(__GNUC__) && (__GNUC__ >= 4)
 #define FREERDP_API __attribute__((visibility("default")))
 #else
 #define FREERDP_API
@@ -65,7 +65,7 @@
 #if defined _WIN32 || defined __CYGWIN__
 #define FREERDP_LOCAL
 #else
-#if __GNUC__ >= 4
+#if defined(__GNUC__) && (__GNUC__ >= 4)
 #define FREERDP_LOCAL __attribute__((visibility("hidden")))
 #else
 #define FREERDP_LOCAL
diff --git a/uwac/include/uwac/uwac.h b/uwac/include/uwac/uwac.h
index 6c660e29d..928e69312 100644
--- a/uwac/include/uwac/uwac.h
+++ b/uwac/include/uwac/uwac.h
@@ -26,7 +26,7 @@
 #include <wayland-client.h>
 #include <stdbool.h>
 
-#if __GNUC__ >= 4
+#if defined(__GNUC__) && (__GNUC__ >= 4)
 #define UWAC_API __attribute__((visibility("default")))
 #else
 #define UWAC_API
diff --git a/winpr/include/winpr/platform.h b/winpr/include/winpr/platform.h
index 7a3028cc8..16276f2e5 100644
--- a/winpr/include/winpr/platform.h
+++ b/winpr/include/winpr/platform.h
@@ -22,7 +22,7 @@
 
 #include <stdlib.h>
 
-#if __clang__
+#if defined(__clang__)
 #define WINPR_PRAGMA_DIAG_PUSH _Pragma("clang diagnostic push")
 #define WINPR_PRAGMA_DIAG_IGNORED_PEDANTIC _Pragma("clang diagnostic ignored \"-Wpedantic\"")
 #define WINPR_PRAGMA_DIAG_IGNORED_MISSING_PROTOTYPES \
@@ -38,7 +38,7 @@
 #define WINPR_PRAGMA_DIAG_IGNORED_FORMAT_SECURITY \
 	_Pragma("clang diagnostic ignored \"-Wformat-security\"")
 #define WINPR_PRAGMA_DIAG_POP _Pragma("clang diagnostic pop")
-#elif __GNUC__
+#elif defined(__GNUC__)
 #define WINPR_PRAGMA_DIAG_PUSH _Pragma("GCC diagnostic push")
 #define WINPR_PRAGMA_DIAG_IGNORED_PEDANTIC _Pragma("GCC diagnostic ignored \"-Wpedantic\"")
 #define WINPR_PRAGMA_DIAG_IGNORED_MISSING_PROTOTYPES \
diff --git a/winpr/include/winpr/winpr.h b/winpr/include/winpr/winpr.h
index dfd999f6d..d9558d862 100644
--- a/winpr/include/winpr/winpr.h
+++ b/winpr/include/winpr/winpr.h
@@ -37,7 +37,7 @@
 #endif
 #endif
 #else
-#if __GNUC__ >= 4
+#if defined(__GNUC__) && (__GNUC__ >= 4)
 #define WINPR_API __attribute__((visibility("default")))
 #else
 #define WINPR_API
@@ -79,7 +79,7 @@
 #if defined _WIN32 || defined __CYGWIN__
 #define WINPR_LOCAL
 #else
-#if __GNUC__ >= 4
+#if defined(__GNUC__) && (__GNUC__ >= 4)
 #define WINPR_LOCAL __attribute__((visibility("hidden")))
 #else
 #define WINPR_LOCAL
diff --git a/winpr/libwinpr/utils/corkscrew/ptrace.h b/winpr/libwinpr/utils/corkscrew/ptrace.h
index 5f981a64c..8ff75753e 100644
--- a/winpr/libwinpr/utils/corkscrew/ptrace.h
+++ b/winpr/libwinpr/utils/corkscrew/ptrace.h
@@ -45,7 +45,7 @@ extern "C"
 		const map_info_t* map_info_list;
 	} memory_t;
 
-#if __i386__
+#ifdef __i386__
 	/* ptrace() register context. */
 	typedef struct pt_regs_x86
 	{
@@ -69,7 +69,7 @@ extern "C"
 	} pt_regs_x86_t;
 #endif
 
-#if __mips__
+#ifdef __mips__
 	/* ptrace() GET_REGS context. */
 	typedef struct pt_regs_mips
 	{