Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -42,28 +42,10 @@
 AX_CHECK_COMPILER_FLAGS(-Wsemicolon-before-method-body,
 	[OBJCFLAGS="$OBJCFLAGS -Wsemicolon-before-method-body"])
 AX_CHECK_COMPILER_FLAGS(-Wno-objc-root-class,
 	[OBJCFLAGS="$OBJCFLAGS -Wno-objc-root-class"])
 
-AC_MSG_CHECKING(whether Objective C compiler supports fast enumeration)
-AC_TRY_COMPILE([
-	@protocol OFFastEnumeration
-	- (int)countByEnumeratingWithState: (void*)state
-				   objects: (id*)objects
-				     count: (int)count;
-	@end
-], [
-	id n = (id)0;
-	for (id i in n);
-], [
-	AC_DEFINE(OF_HAVE_FAST_ENUMERATION, 1,
-		[Compiler support for Fast Enumeration])
-	AC_MSG_RESULT(yes)
-], [
-	AC_MSG_RESULT(no)
-])
-
 AC_MSG_CHECKING(whether Objective C compiler supports properties)
 AC_TRY_COMPILE([
 	@interface Foo
 	{
 		id bar;
@@ -74,36 +56,13 @@
 ], [
 	Foo *foo = (id)0;
 	[foo setBar: (id)0];
 	[foo bar];
 ], [
-	AC_DEFINE(OF_HAVE_PROPERTIES, 1, [Compiler support for properties])
 	AC_SUBST(PROPERTIESTESTS_M, "PropertiesTests.m")
 	AC_MSG_RESULT(yes)
 ], [
-	AC_MSG_RESULT(no)
-])
-
-AC_MSG_CHECKING(whether Objective C compiler supports optional protocols)
-AC_TRY_COMPILE([
-	@protocol Proto
-	@optional
-	+ (void)foo;
-	@end
-
-	@interface Foo <Proto>
-	@end
-
-	@implementation Foo
-	@end
-], [
-	[Foo foo];
-], [
-	AC_DEFINE(OF_HAVE_OPTIONAL_PROTOCOLS, 1,
-		[Compiler support for optional protocols])
-	AC_MSG_RESULT(yes)
-], [
 	AC_MSG_RESULT(no)
 ])
 
 AC_MSG_CHECKING(whether Objective C compiler supports blocks)
 old_OBJCFLAGS="$OBJCFLAGS"
@@ -110,11 +69,10 @@
 OBJCFLAGS="$OBJCFLAGS -fblocks"
 AC_TRY_COMPILE([], [
 	int (^foo)(int bar);
 	foo = ^ (int bar) { return 0; }
 ], [
-	AC_DEFINE(OF_HAVE_BLOCKS, 1, [Compiler support for blocks])
 	AC_SUBST(BLOCKS_FLAGS, "-fblocks")
 	AC_SUBST(OFBLOCKTESTS_M, "OFBlockTests.m")
 	AC_MSG_RESULT(yes)
 ], [
 	AC_MSG_RESULT(no)

Index: src/OFObject.h
==================================================================
--- src/OFObject.h
+++ src/OFObject.h
@@ -44,10 +44,26 @@
 #endif
 
 #ifndef __has_feature
 # define __has_feature(x) 0
 #endif
+
+#if defined(__clang__)
+# define OF_HAVE_PROPERTIES
+# define OF_HAVE_OPTIONAL_PROTOCOLS
+# define OF_HAVE_FAST_ENUMERATION
+#elif defined(__GNUC__)
+# if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
+#  define OF_HAVE_PROPERTIES
+#  define OF_HAVE_OPTIONAL_PROTOCOLS
+#  define OF_HAVE_FAST_ENUMERATION
+# endif
+#endif
+
+#if __has_feature(blocks)
+# define OF_HAVE_BLOCKS
+#endif
 
 #if __has_feature(objc_bool)
 # undef YES
 # define YES __objc_yes
 # undef NO

Index: src/objfw-defs.h.in
==================================================================
--- src/objfw-defs.h.in
+++ src/objfw-defs.h.in
@@ -2,21 +2,17 @@
 #undef OF_ATOMIC_OPS
 #undef OF_BIG_ENDIAN
 #undef OF_COMPILER_TLS
 #undef OF_FLOAT_BIG_ENDIAN
 #undef OF_HAVE_ASPRINTF
-#undef OF_HAVE_BLOCKS
-#undef OF_HAVE_FAST_ENUMERATION
 #undef OF_HAVE_GCC_ATOMIC_OPS
-#undef OF_HAVE_OPTIONAL_PROTOCOLS
 #undef OF_HAVE_OSATOMIC
 #undef OF_HAVE_OSATOMIC_64
-#undef OF_HAVE_PROPERTIES
 #undef OF_HAVE_PTHREADS
 #undef OF_HAVE_PTHREAD_SPINLOCKS
 #undef OF_HAVE_RECURSIVE_PTHREAD_MUTEXES
 #undef OF_HAVE_SCHED_YIELD
 #undef OF_HAVE_SYS_SELECT_H
 #undef OF_OBJFW_RUNTIME
 #undef OF_PLUGINS
 #undef OF_THREADS
 #undef SIZE_MAX