diff --git a/config.lib b/config.lib
index ab9bb82b61..a144b9e3ea 100644
--- a/config.lib
+++ b/config.lib
@@ -1285,7 +1285,7 @@ make_compiler_cflags() {
 
 		# -W alone doesn't enable all warnings enabled by -Wall; on the other hand,
 		# -Weverything enables too many useless warnings that can't be disabled (as of 3.0)
-		flags="$flags -Wall -W"
+		flags="$flags -Wall -W -Wextra"
 
 		# warning: unused parameter '...'
 		flags="$flags -Wno-unused-parameter"
@@ -1326,6 +1326,11 @@ make_compiler_cflags() {
 			flags="$flags -Wno-unused-variable"
 		fi
 
+		if [ "$cc_version" -ge "33" ]; then
+			# clang completed C++11 support in version 3.3
+			flags="$flags -std=c++11"
+		fi
+
 		# rdynamic is used to get useful stack traces from crash reports.
 		ldflags="$ldflags -rdynamic"
 	else
diff --git a/src/table/newgrf_debug_data.h b/src/table/newgrf_debug_data.h
index b7d0c92024..afe19bbedb 100644
--- a/src/table/newgrf_debug_data.h
+++ b/src/table/newgrf_debug_data.h
@@ -17,7 +17,7 @@
 #define NIP_END() { NULL, 0, 0, 0, 0 }
 
 /* Helper for filling callback tables */
-#define NIC(cb_id, base, variable, bit) { #cb_id, cpp_offsetof(base, variable), cpp_sizeof(base, variable), bit, cb_id }
+#define NIC(cb_id, base, variable, bit) { #cb_id, (ptrdiff_t)cpp_offsetof(base, variable), cpp_sizeof(base, variable), bit, cb_id }
 #define NIC_END() { NULL, 0, 0, 0, 0 }
 
 /* Helper for filling variable tables */