diff --git a/ChangeLog b/ChangeLog
index 66603c02a..fad9d0b22 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2016-12-22  Werner Lemberg  <wl@gnu.org>
+
+	Ensure used preprocessor symbols are defined (#49790).
+
+	* builds/unix/ftconfig.in, builds/vms/ftconfig.h,
+	include/freetype/config/ftconfig.h: Check `__GNUC__', `__IBMC__',
+	and `__SUNPRO_C' correctly.
+
 2016-12-22  Werner Lemberg  <wl@gnu.org>
 
 	* src/base/ftrfork.c (FT_Raccess_Get_DataOffsets): Check `count'.
diff --git a/builds/unix/ftconfig.in b/builds/unix/ftconfig.in
index 6f228f51f..6401f657c 100644
--- a/builds/unix/ftconfig.in
+++ b/builds/unix/ftconfig.in
@@ -378,9 +378,10 @@ FT_BEGIN_HEADER
 
 
   /* typeof condition taken from gnulib's `intprops.h' header file */
-#if ( __GNUC__ >= 2                                      || \
-      ( __IBMC__ >= 1210 && defined( __IBM__TYPEOF__ ) ) || \
-      ( __SUNPRO_C >= 0x5110 && !__STDC__ )              )
+#if ( ( defined( __GNUC__ ) && __GNUC__ >= 2 )                       || \
+      ( defined( __IBMC__ ) && __IBMC__ >= 1210 &&                      \
+        defined( __IBM__TYPEOF__ ) )                                 || \
+      ( defined( __SUNPRO_C ) && __SUNPRO_C >= 0x5110 && !__STDC__ ) )
 #define FT_TYPEOF( type )  ( __typeof__ ( type ) )
 #else
 #define FT_TYPEOF( type )  /* empty */
diff --git a/builds/vms/ftconfig.h b/builds/vms/ftconfig.h
index 9c7e4eca9..eb7fced3a 100644
--- a/builds/vms/ftconfig.h
+++ b/builds/vms/ftconfig.h
@@ -319,9 +319,10 @@ FT_BEGIN_HEADER
 
 
   /* typeof condition taken from gnulib's `intprops.h' header file */
-#if ( __GNUC__ >= 2                                      || \
-      ( __IBMC__ >= 1210 && defined( __IBM__TYPEOF__ ) ) || \
-      ( __SUNPRO_C >= 0x5110 && !__STDC__ )              )
+#if ( ( defined( __GNUC__ ) && __GNUC__ >= 2 )                       || \
+      ( defined( __IBMC__ ) && __IBMC__ >= 1210 &&                      \
+        defined( __IBM__TYPEOF__ ) )                                 || \
+      ( defined( __SUNPRO_C ) && __SUNPRO_C >= 0x5110 && !__STDC__ ) )
 #define FT_TYPEOF( type )  ( __typeof__ ( type ) )
 #else
 #define FT_TYPEOF( type )  /* empty */
diff --git a/include/freetype/config/ftconfig.h b/include/freetype/config/ftconfig.h
index 7c21d66c9..62b807f63 100644
--- a/include/freetype/config/ftconfig.h
+++ b/include/freetype/config/ftconfig.h
@@ -346,9 +346,10 @@ FT_BEGIN_HEADER
 
 
   /* typeof condition taken from gnulib's `intprops.h' header file */
-#if ( __GNUC__ >= 2                                      || \
-      ( __IBMC__ >= 1210 && defined( __IBM__TYPEOF__ ) ) || \
-      ( __SUNPRO_C >= 0x5110 && !__STDC__ )              )
+#if ( ( defined( __GNUC__ ) && __GNUC__ >= 2 )                       || \
+      ( defined( __IBMC__ ) && __IBMC__ >= 1210 &&                      \
+        defined( __IBM__TYPEOF__ ) )                                 || \
+      ( defined( __SUNPRO_C ) && __SUNPRO_C >= 0x5110 && !__STDC__ ) )
 #define FT_TYPEOF( type )  ( __typeof__ ( type ) )
 #else
 #define FT_TYPEOF( type )  /* empty */