diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4d154e4..f9ea663 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -105,6 +105,7 @@ add_library(base64
     # library files
     lib/lib.c
     lib/codec_choose.c
+    lib/feature_level.c
     include/libbase64.h
 
     lib/tables/tables.c
diff --git a/Makefile b/Makefile
index bba3fde..79d91a1 100644
--- a/Makefile
+++ b/Makefile
@@ -15,6 +15,7 @@ OBJS = \
   lib/arch/avx/codec.o \
   lib/lib.o \
   lib/codec_choose.o \
+  lib/feature_level.o \
   lib/tables/tables.o
 
 HAVE_AVX512 = 0
diff --git a/lib/codec_choose.c b/lib/codec_choose.c
index 8b5938d..941117e 100644
--- a/lib/codec_choose.c
+++ b/lib/codec_choose.c
@@ -16,76 +16,6 @@
   #endif
 #endif
 
-#ifdef BASE64_X86
-#ifdef _MSC_VER
-	#include <intrin.h>
-	#define __cpuid_count(__level, __count, __eax, __ebx, __ecx, __edx) \
-	{						\
-		int info[4];				\
-		__cpuidex(info, __level, __count);	\
-		__eax = info[0];			\
-		__ebx = info[1];			\
-		__ecx = info[2];			\
-		__edx = info[3];			\
-	}
-	#define __cpuid(__level, __eax, __ebx, __ecx, __edx) \
-		__cpuid_count(__level, 0, __eax, __ebx, __ecx, __edx)
-#else
-	#include <cpuid.h>
-	#if HAVE_AVX512 || HAVE_AVX2 || HAVE_AVX
-		#if ((__GNUC__ > 4 || __GNUC__ == 4 && __GNUC_MINOR__ >= 2) || (__clang_major__ >= 3))
-			static inline uint64_t _xgetbv (uint32_t index)
-			{
-				uint32_t eax, edx;
-				__asm__ __volatile__("xgetbv" : "=a"(eax), "=d"(edx) : "c"(index));
-				return ((uint64_t)edx << 32) | eax;
-			}
-		#else
-			#error "Platform not supported"
-		#endif
-	#endif
-#endif
-
-#ifndef bit_AVX512vl
-#define bit_AVX512vl (1 << 31)
-#endif
-#ifndef bit_AVX512vbmi
-#define bit_AVX512vbmi (1 << 1)
-#endif
-#ifndef bit_AVX2
-#define bit_AVX2 (1 << 5)
-#endif
-#ifndef bit_SSSE3
-#define bit_SSSE3 (1 << 9)
-#endif
-#ifndef bit_SSE41
-#define bit_SSE41 (1 << 19)
-#endif
-#ifndef bit_SSE42
-#define bit_SSE42 (1 << 20)
-#endif
-#ifndef bit_AVX
-#define bit_AVX (1 << 28)
-#endif
-
-#define bit_XSAVE_XRSTORE (1 << 27)
-
-#ifndef _XCR_XFEATURE_ENABLED_MASK
-#define _XCR_XFEATURE_ENABLED_MASK 0
-#endif
-
-#define bit_XMM      (1 << 1)
-#define bit_YMM      (1 << 2)
-#define bit_OPMASK   (1 << 5)
-#define bit_ZMM      (1 << 6)
-#define bit_HIGH_ZMM (1 << 7)
-
-#define _XCR_XMM_AND_YMM_STATE_ENABLED_BY_OS (bit_XMM | bit_YMM)
-
-#define _AVX_512_ENABLED_BY_OS (bit_XMM | bit_YMM | bit_OPMASK | bit_ZMM | bit_HIGH_ZMM)
-
-#endif
-
 // Function declarations:
 #define BASE64_CODEC_FUNCS(arch)					\
 	extern void base64_stream_encode_ ## arch BASE64_ENC_PARAMS;	\
@@ -185,113 +115,35 @@ codec_choose_arm (struct codec *codec)
 #endif
 }
 
-static bool
-codec_choose_x86 (struct codec *codec)
-{
 #ifdef BASE64_X86_SIMD
 
-	unsigned int eax, ebx = 0, ecx = 0, edx;
-	unsigned int max_level;
-
-	#ifdef _MSC_VER
-	int info[4];
-	__cpuidex(info, 0, 0);
-	max_level = info[0];
-	#else
-	max_level = __get_cpuid_max(0, NULL);
-	#endif
+static const int cpu_feature_flags[X86_FEATURE_LEVEL_COUNT] = {
+	[X86_FEATURE_LEVEL_NONE]   = 0,
+	[X86_FEATURE_LEVEL_SSSE3]  = BASE64_FORCE_SSSE3,
+	[X86_FEATURE_LEVEL_SSE41]  = BASE64_FORCE_SSE41,
+	[X86_FEATURE_LEVEL_SSE42]  = BASE64_FORCE_SSE42,
+	[X86_FEATURE_LEVEL_AVX]    = BASE64_FORCE_AVX,
+	[X86_FEATURE_LEVEL_AVX2]   = BASE64_FORCE_AVX2,
+	[X86_FEATURE_LEVEL_AVX512] = BASE64_FORCE_AVX512
+};
 
-	#if HAVE_AVX512 || HAVE_AVX2 || HAVE_AVX
-	// Check for AVX/AVX2/AVX512 support:
-	// Checking for AVX requires 3 things:
-	// 1) CPUID indicates that the OS uses XSAVE and XRSTORE instructions
-	//    (allowing saving YMM registers on context switch)
-	// 2) CPUID indicates support for AVX
-	// 3) XGETBV indicates the AVX registers will be saved and restored on
-	//    context switch
-	//
-	// Note that XGETBV is only available on 686 or later CPUs, so the
-	// instruction needs to be conditionally run.
-	if (max_level >= 1) {
-		__cpuid_count(1, 0, eax, ebx, ecx, edx);
-		if (ecx & bit_XSAVE_XRSTORE) {
-			uint64_t xcr_mask;
-			xcr_mask = _xgetbv(_XCR_XFEATURE_ENABLED_MASK);
-			if ((xcr_mask & _XCR_XMM_AND_YMM_STATE_ENABLED_BY_OS) == _XCR_XMM_AND_YMM_STATE_ENABLED_BY_OS) { // check multiple bits at once
-				#if HAVE_AVX512
-				if (max_level >= 7 && ((xcr_mask & _AVX_512_ENABLED_BY_OS) == _AVX_512_ENABLED_BY_OS)) {
-					__cpuid_count(7, 0, eax, ebx, ecx, edx);
-					if ((ebx & bit_AVX512vl) && (ecx & bit_AVX512vbmi)) {
-						codec->enc = base64_stream_encode_avx512;
-						codec->dec = base64_stream_decode_avx512;
-						return true;
-					}
-				}
-				#endif
-				#if HAVE_AVX2
-				if (max_level >= 7) {
-					__cpuid_count(7, 0, eax, ebx, ecx, edx);
-					if (ebx & bit_AVX2) {
-						codec->enc = base64_stream_encode_avx2;
-						codec->dec = base64_stream_decode_avx2;
-						return true;
-					}
-				}
-				#endif
-				#if HAVE_AVX
-				__cpuid_count(1, 0, eax, ebx, ecx, edx);
-				if (ecx & bit_AVX) {
-					codec->enc = base64_stream_encode_avx;
-					codec->dec = base64_stream_decode_avx;
-					return true;
-				}
-				#endif
-			}
-		}
-	}
-	#endif
-
-	#if HAVE_SSE42
-	// Check for SSE42 support:
-	if (max_level >= 1) {
-		__cpuid(1, eax, ebx, ecx, edx);
-		if (ecx & bit_SSE42) {
-			codec->enc = base64_stream_encode_sse42;
-			codec->dec = base64_stream_decode_sse42;
-			return true;
-		}
-	}
-	#endif
+#endif // BASE64_X86
 
-	#if HAVE_SSE41
-	// Check for SSE41 support:
-	if (max_level >= 1) {
-		__cpuid(1, eax, ebx, ecx, edx);
-		if (ecx & bit_SSE41) {
-			codec->enc = base64_stream_encode_sse41;
-			codec->dec = base64_stream_decode_sse41;
-			return true;
-		}
-	}
-	#endif
+static bool
+codec_choose_x86 (struct codec *codec)
+{
+#ifdef BASE64_X86_SIMD
+	int feature_level;
 
-	#if HAVE_SSSE3
-	// Check for SSSE3 support:
-	if (max_level >= 1) {
-		__cpuid(1, eax, ebx, ecx, edx);
-		if (ecx & bit_SSSE3) {
-			codec->enc = base64_stream_encode_ssse3;
-			codec->dec = base64_stream_decode_ssse3;
-			return true;
-		}
-	}
-	#endif
+	feature_level = x86_get_cpu_feature_level();
+	codec_choose_forced(codec, cpu_feature_flags[feature_level]);
+	return true;
 
 #else
 	(void)codec;
-#endif
 
 	return false;
+#endif // BASE64_X86_SIMD
 }
 
 void
diff --git a/lib/codecs.h b/lib/codecs.h
index f6af0e7..61469c6 100644
--- a/lib/codecs.h
+++ b/lib/codecs.h
@@ -55,3 +55,20 @@ struct codec
 };
 
 extern void codec_choose (struct codec *, int flags);
+
+#if (__x86_64__ || __i386__ || _M_X86 || _M_X64)
+enum
+{
+	X86_FEATURE_LEVEL_NONE,
+	X86_FEATURE_LEVEL_SSSE3,
+	X86_FEATURE_LEVEL_SSE41,
+	X86_FEATURE_LEVEL_SSE42,
+	X86_FEATURE_LEVEL_AVX,
+	X86_FEATURE_LEVEL_AVX2,
+	X86_FEATURE_LEVEL_AVX512,
+
+	X86_FEATURE_LEVEL_COUNT
+};
+
+extern int x86_get_cpu_feature_level (void);
+#endif // (__x86_64__ || __i386__ || _M_X86 || _M_X64)
diff --git a/lib/feature_level.c b/lib/feature_level.c
new file mode 100644
index 0000000..47da0e6
--- /dev/null
+++ b/lib/feature_level.c
@@ -0,0 +1,183 @@
+#include <stdbool.h>
+#include <stdint.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+
+#include "../include/libbase64.h"
+#include "codecs.h"
+#include "config.h"
+#include "env.h"
+
+#if (__x86_64__ || __i386__ || _M_X86 || _M_X64)
+  #define BASE64_X86
+  #if (HAVE_SSSE3 || HAVE_SSE41 || HAVE_SSE42 || HAVE_AVX || HAVE_AVX2 || HAVE_AVX512)
+    #define BASE64_X86_SIMD
+  #endif
+#endif
+
+#ifdef BASE64_X86
+#ifdef _MSC_VER
+	#include <intrin.h>
+	#define __cpuid_count(__level, __count, __eax, __ebx, __ecx, __edx) \
+	{						\
+		int info[4];				\
+		__cpuidex(info, __level, __count);	\
+		__eax = info[0];			\
+		__ebx = info[1];			\
+		__ecx = info[2];			\
+		__edx = info[3];			\
+	}
+	#define __cpuid(__level, __eax, __ebx, __ecx, __edx) \
+		__cpuid_count(__level, 0, __eax, __ebx, __ecx, __edx)
+#else
+	#include <cpuid.h>
+	#if HAVE_AVX512 || HAVE_AVX2 || HAVE_AVX
+		#if ((__GNUC__ > 4 || __GNUC__ == 4 && __GNUC_MINOR__ >= 2) || (__clang_major__ >= 3))
+			static inline uint64_t _xgetbv (uint32_t index)
+			{
+				uint32_t eax, edx;
+				__asm__ __volatile__("xgetbv" : "=a"(eax), "=d"(edx) : "c"(index));
+				return ((uint64_t)edx << 32) | eax;
+			}
+		#else
+			#error "Platform not supported"
+		#endif
+	#endif
+#endif
+
+#ifndef bit_AVX512vl
+#define bit_AVX512vl (1 << 31)
+#endif
+#ifndef bit_AVX512vbmi
+#define bit_AVX512vbmi (1 << 1)
+#endif
+#ifndef bit_AVX2
+#define bit_AVX2 (1 << 5)
+#endif
+#ifndef bit_SSSE3
+#define bit_SSSE3 (1 << 9)
+#endif
+#ifndef bit_SSE41
+#define bit_SSE41 (1 << 19)
+#endif
+#ifndef bit_SSE42
+#define bit_SSE42 (1 << 20)
+#endif
+#ifndef bit_AVX
+#define bit_AVX (1 << 28)
+#endif
+
+#define bit_XSAVE_XRSTORE (1 << 27)
+
+#ifndef _XCR_XFEATURE_ENABLED_MASK
+#define _XCR_XFEATURE_ENABLED_MASK 0
+#endif
+
+#define bit_XMM      (1 << 1)
+#define bit_YMM      (1 << 2)
+#define bit_OPMASK   (1 << 5)
+#define bit_ZMM      (1 << 6)
+#define bit_HIGH_ZMM (1 << 7)
+
+#define _XCR_XMM_AND_YMM_STATE_ENABLED_BY_OS (bit_XMM | bit_YMM)
+
+#define _AVX_512_ENABLED_BY_OS (bit_XMM | bit_YMM | bit_OPMASK | bit_ZMM | bit_HIGH_ZMM)
+
+#endif
+
+#ifdef BASE64_X86
+
+int x86_get_cpu_feature_level (void)
+{
+	unsigned int eax, ebx, ecx, edx;
+	unsigned int max_level;
+
+#ifdef _MSC_VER
+	int info[4];
+	__cpuidex(info, 0, 0);
+	max_level = info[0];
+#else
+	max_level = __get_cpuid_max(0, NULL);
+#endif
+
+	if (max_level >= 1) {
+
+#if HAVE_AVX512 || HAVE_AVX2 || HAVE_AVX
+		// Check for AVX/AVX2/AVX512 support:
+		// Checking for AVX requires 3 things:
+		// 1) CPUID indicates that the OS uses XSAVE and XRSTORE instructions
+		//    (allowing saving YMM registers on context switch)
+		// 2) CPUID indicates support for AVX
+		// 3) XGETBV indicates the AVX registers will be saved and restored on
+		//    context switch
+		//
+		// Note that XGETBV is only available on 686 or later CPUs, so the
+		// instruction needs to be conditionally run.
+		__cpuid_count(1, 0, eax, ebx, ecx, edx);
+		if (ecx & bit_XSAVE_XRSTORE) {
+			uint64_t xcr_mask;
+			xcr_mask = _xgetbv(_XCR_XFEATURE_ENABLED_MASK);
+			if ((xcr_mask & _XCR_XMM_AND_YMM_STATE_ENABLED_BY_OS) == _XCR_XMM_AND_YMM_STATE_ENABLED_BY_OS) { // check multiple bits at once
+#if HAVE_AVX512
+				if (max_level >= 7 && ((xcr_mask & _AVX_512_ENABLED_BY_OS) == _AVX_512_ENABLED_BY_OS)) {
+					__cpuid_count(7, 0, eax, ebx, ecx, edx);
+					if ((ebx & bit_AVX512vl) && (ecx & bit_AVX512vbmi)) {
+						return X86_FEATURE_LEVEL_AVX512;
+					}
+				}
+#endif // HAVE_AVX512
+
+#if HAVE_AVX2
+				if (max_level >= 7) {
+					__cpuid_count(7, 0, eax, ebx, ecx, edx);
+					if (ebx & bit_AVX2) {
+						return X86_FEATURE_LEVEL_AVX2;
+					}
+				}
+#endif // HAVE_AVX2
+
+#if HAVE_AVX
+				__cpuid_count(1, 0, eax, ebx, ecx, edx);
+				if (ecx & bit_AVX) {
+					return X86_FEATURE_LEVEL_AVX;
+				}
+#endif // HAVE_AVX
+			}
+		}
+#endif // HAVE_AVX512 || HAVE_AVX2 || HAVE_AVX
+
+		__cpuid(1, eax, ebx, ecx, edx);
+
+#if HAVE_SSE42
+		// Check for SSE42 support:
+		if (ecx & bit_SSE42) {
+			return X86_FEATURE_LEVEL_SSE42;
+		}
+#endif // HAVE_SSE42
+
+#if HAVE_SSE41
+		// Check for SSE41 support:
+		if (ecx & bit_SSE41) {
+			return X86_FEATURE_LEVEL_SSE41;
+		}
+#endif // HAVE_SSE41
+
+#if HAVE_SSSE3
+		// Check for SSSE3 support:
+		if (ecx & bit_SSSE3) {
+			return X86_FEATURE_LEVEL_SSSE3;
+		}
+#endif // HAVE_SSSE3
+	}
+
+	return X86_FEATURE_LEVEL_NONE;
+}
+#else
+
+int x86_get_cpu_feature_level (void)
+{
+	return X86_FEATURE_LEVEL_NONE;
+}
+
+#endif // BASE64_X86
diff --git a/test/Makefile b/test/Makefile
index 7ecb893..7dbe4cc 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -22,10 +22,13 @@ test: clean test_base64 benchmark
 valgrind: clean test_base64
 	valgrind --error-exitcode=2 ./test_base64
 
-test_base64: test_base64.c codec_supported.o ../lib/libbase64.o
+feature_level.o: ../lib/feature_level.c ../lib/config.h
+	$(CC) $(CFLAGS) -o $@ -c $<
+
+test_base64: test_base64.c codec_supported.o feature_level.o ../lib/libbase64.o
 	$(CC) $(CFLAGS) -o $@ $^
 
-benchmark: benchmark.c codec_supported.o ../lib/libbase64.o
+benchmark: benchmark.c codec_supported.o feature_level.o ../lib/libbase64.o
 	$(CC) $(CFLAGS) -o $@ $^ $(BENCH_LDFLAGS)
 
 ../%:
diff --git a/test/codec_supported.c b/test/codec_supported.c
index e90d820..5910d8b 100644
--- a/test/codec_supported.c
+++ b/test/codec_supported.c
@@ -3,6 +3,40 @@
 #include <string.h>
 
 #include "../include/libbase64.h"
+#include "../lib/codecs.h"
+
+static int
+cpu_has_x86_extension (const char *codec)
+{
+#if (__x86_64__ || __i386__ || _M_X86 || _M_X64)
+	int feature_level;
+
+	feature_level = x86_get_cpu_feature_level();
+
+	if (strcmp(codec, "SSSE3") == 0) {
+		return feature_level >= X86_FEATURE_LEVEL_SSSE3;
+	}
+	if (strcmp(codec, "SSE41") == 0) {
+		return feature_level >= X86_FEATURE_LEVEL_SSE41;
+	}
+	if (strcmp(codec, "SSE42") == 0) {
+		return feature_level >= X86_FEATURE_LEVEL_SSE42;
+	}
+	if (strcmp(codec, "AVX") == 0) {
+		return feature_level >= X86_FEATURE_LEVEL_AVX;
+	}
+	if (strcmp(codec, "AVX2") == 0) {
+		return feature_level >= X86_FEATURE_LEVEL_AVX2;
+	}
+	if (strcmp(codec, "AVX512") == 0) {
+		return feature_level >= X86_FEATURE_LEVEL_AVX512;
+	}
+	return 0;
+#else
+	(void)codec;
+	return 0;
+#endif
+}
 
 static char *_codecs[] =
 { "AVX2"
@@ -25,6 +59,12 @@ codec_supported (size_t index)
 	if (index >= (sizeof(_codecs) / sizeof(_codecs[0])) - 1) {
 		return 0;
 	}
+
+	// Early out if CPU extension is not present:
+	if (!cpu_has_x86_extension(_codecs[index])) {
+		return 0;
+	}
+
 	// Check if given codec is supported by trying to decode a test string:
 	char *a = "aGVsbG8=";
 	char b[10];