diff --git a/CMakeLists.txt b/CMakeLists.txt
index bc6752b..8a51376 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -17,6 +17,7 @@ option(ENABLE_STATIC "Build a static version of the libraries?" OFF)
 option(DISABLE_SHARED "Do not build a shared version of the libraries?" OFF)
 option(ENABLE_TESTING "Enable ctest?" OFF)
 option(ENABLE_BENCHMARK "Enable benchmark?" OFF)
+option(LITTLE_ENDIAN_CTR "little-endian ctr mode" OFF)
 
 
 # simon speck build options
@@ -133,6 +134,11 @@ if(ENABLE_AVX2)
     endif()
 endif()
 
+# flags
+if(LITTLE_ENDIAN_CTR)
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DLITTLE_ENDIAN_CTR")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DLITTLE_ENDIAN_CTR")
+endif()
 
 # source
 set(libspeck_SRCS ${libspeck_SRCS} src/speck/speck_common.c)
diff --git a/src/speck/speck_ctr.c b/src/speck/speck_ctr.c
index e2523c8..178c65a 100644
--- a/src/speck/speck_ctr.c
+++ b/src/speck/speck_ctr.c
@@ -42,11 +42,21 @@ int speck_ctr_encrypt(speck_ctx_t *ctx, const uint8_t *in, uint8_t *out, int len
     uint64_t crypted_iv_block[2];
     uint64_t plain_block[2];
     uint64_t iv_block[2];
+#ifdef LITTLE_ENDIAN_CTR
+    uint64_t iv_tmp[2];
+    iv_tmp[0] = ((uint64_t*)iv)[0];
+    iv_tmp[1] = ((uint64_t*)iv)[1];
+#endif
     for (i = 0; i < count; i++) {
+#ifdef LITTLE_ENDIAN_CTR
+        iv_block[0] = iv_tmp[0];
+        iv_block[1] = iv_tmp[1];
+        iv_tmp[0]++;
+#else
         cast_uint8_array_to_uint64(&iv_block[0], iv + (WORDS * 0));
         cast_uint8_array_to_uint64(&iv_block[1], iv + (WORDS * 1));
         ctr128_inc(iv);
-
+#endif
         speck_encrypt(ctx, iv_block, crypted_iv_block);
 
         int array_idx = (i * (BLOCK_SIZE * LANE_NUM));
@@ -60,9 +70,15 @@ int speck_ctr_encrypt(speck_ctx_t *ctx, const uint8_t *in, uint8_t *out, int len
         cast_uint64_to_uint8_array(cur_crypted + (WORDS * 1), crypted_iv_block[1] ^ plain_block[1]);
     }
     if (remain_bytes != 0) {
+#ifdef LITTLE_ENDIAN_CTR
+        iv_block[0] = iv_tmp[0];
+        iv_block[1] = iv_tmp[1];
+        iv_tmp[0]++;
+#else
         cast_uint8_array_to_uint64(&iv_block[0], iv + (WORDS * 0));
         cast_uint8_array_to_uint64(&iv_block[1], iv + (WORDS * 1));
         ctr128_inc(iv);
+#endif
 
         speck_encrypt(ctx, iv_block, crypted_iv_block);
 
@@ -84,6 +100,11 @@ int speck_ctr_encrypt(speck_ctx_t *ctx, const uint8_t *in, uint8_t *out, int len
         }
     }
 
+#ifdef LITTLE_ENDIAN_CTR
+    cast_uint64_to_uint8_array(iv + (WORDS * 0), iv_tmp[0]);
+    cast_uint64_to_uint8_array(iv + (WORDS * 1), iv_tmp[1]);
+#endif
+
     return 0;
 }