diff --git a/src/core/coding/ojph_block_encoder.cpp b/src/core/coding/ojph_block_encoder.cpp
index f9c8d89..019f4f1 100644
--- a/src/core/coding/ojph_block_encoder.cpp
+++ b/src/core/coding/ojph_block_encoder.cpp
@@ -44,6 +44,7 @@
 #include <cstring>
 #include <cstdint>
 #include <climits>
+#include <mutex>
 
 #include "ojph_mem.h"
 #include "ojph_arch.h"
@@ -253,17 +254,16 @@ namespace ojph {
       return true;
     }
 
-    /////////////////////////////////////////////////////////////////////////
-    static bool tables_initialized = false;
-
     /////////////////////////////////////////////////////////////////////////
     bool initialize_block_encoder_tables() {
-      if (!tables_initialized) {
+      static bool tables_initialized = false;
+      static std::once_flag tables_initialized_flag;
+      std::call_once(tables_initialized_flag, []() {
         memset(vlc_tbl0, 0, 2048 * sizeof(ui16));
         memset(vlc_tbl1, 0, 2048 * sizeof(ui16));
         tables_initialized = vlc_init_tables();
         tables_initialized = tables_initialized && uvlc_init_tables();
-      }
+      });
       return tables_initialized;
     }
 
diff --git a/src/core/coding/ojph_block_encoder_avx2.cpp b/src/core/coding/ojph_block_encoder_avx2.cpp
index 1bc7a43..91d0195 100644
--- a/src/core/coding/ojph_block_encoder_avx2.cpp
+++ b/src/core/coding/ojph_block_encoder_avx2.cpp
@@ -42,6 +42,7 @@
 #include <cstdint>
 #include <climits>
 #include <immintrin.h>
+#include <mutex>
 
 #include "ojph_mem.h"
 #include "ojph_arch.h"
@@ -220,17 +221,16 @@ namespace ojph {
       return true;
     }
 
-    /////////////////////////////////////////////////////////////////////////
-    static bool tables_initialized = false;
-
     /////////////////////////////////////////////////////////////////////////
     bool initialize_block_encoder_tables_avx2() {
-      if (!tables_initialized) {
+      static bool tables_initialized = false;
+      static std::once_flag tables_initialized_flag;
+      std::call_once(tables_initialized_flag, []() {
         memset(vlc_tbl0, 0, 2048 * sizeof(ui32));
         memset(vlc_tbl1, 0, 2048 * sizeof(ui32));
         tables_initialized = vlc_init_tables();
         tables_initialized = tables_initialized && uvlc_init_tables();
-      }
+      });
       return tables_initialized;
     }
 
diff --git a/src/core/coding/ojph_block_encoder_avx512.cpp b/src/core/coding/ojph_block_encoder_avx512.cpp
index 6de1f3b..3ae7684 100644
--- a/src/core/coding/ojph_block_encoder_avx512.cpp
+++ b/src/core/coding/ojph_block_encoder_avx512.cpp
@@ -42,6 +42,7 @@
 #include <cstdint>
 #include <climits>
 #include <immintrin.h>
+#include <mutex>
 
 #include "ojph_mem.h"
 #include "ojph_block_encoder.h"
@@ -219,17 +220,16 @@ namespace ojph {
       return true;
     }
 
-    /////////////////////////////////////////////////////////////////////////
-    static bool tables_initialized = false;
-
     /////////////////////////////////////////////////////////////////////////
     bool initialize_block_encoder_tables_avx512() {
-      if (!tables_initialized) {
+      static bool tables_initialized = false;
+      static std::once_flag tables_initialized_flag;
+      std::call_once(tables_initialized_flag, []() {
         memset(vlc_tbl0, 0, 2048 * sizeof(ui32));
         memset(vlc_tbl1, 0, 2048 * sizeof(ui32));
         tables_initialized = vlc_init_tables();
         tables_initialized = tables_initialized && uvlc_init_tables();
-      }
+      });
       return tables_initialized;
     }
 
diff --git a/src/core/transform/ojph_colour.cpp b/src/core/transform/ojph_colour.cpp
index b3c05ae..ef147ad 100644
--- a/src/core/transform/ojph_colour.cpp
+++ b/src/core/transform/ojph_colour.cpp
@@ -37,6 +37,7 @@
 
 #include <cmath>
 #include <climits>
+#include <mutex>
 
 #include "ojph_defs.h"
 #include "ojph_arch.h"
@@ -104,27 +105,23 @@ namespace ojph {
       (const float *y, const float *cb, const float *cr,
        float *r, float *g, float *b, ui32 repeat) = NULL;
 
-    //////////////////////////////////////////////////////////////////////////
-    static bool colour_transform_functions_initialized = false;
-
     //////////////////////////////////////////////////////////////////////////
     void init_colour_transform_functions()
     {
-      if (colour_transform_functions_initialized)
-        return;
-
+      static std::once_flag colour_transform_functions_init_flag;
+      std::call_once(colour_transform_functions_init_flag, []() {
 #if !defined(OJPH_ENABLE_WASM_SIMD) || !defined(OJPH_EMSCRIPTEN)
 
-      rev_convert = gen_rev_convert;
-      rev_convert_nlt_type3 = gen_rev_convert_nlt_type3;
-      irv_convert_to_integer = gen_irv_convert_to_integer;
-      irv_convert_to_float = gen_irv_convert_to_float;
-      irv_convert_to_integer_nlt_type3 = gen_irv_convert_to_integer_nlt_type3;
-      irv_convert_to_float_nlt_type3 = gen_irv_convert_to_float_nlt_type3;
-      rct_forward = gen_rct_forward;
-      rct_backward = gen_rct_backward;
-      ict_forward = gen_ict_forward;
-      ict_backward = gen_ict_backward;
+        rev_convert = gen_rev_convert;
+        rev_convert_nlt_type3 = gen_rev_convert_nlt_type3;
+        irv_convert_to_integer = gen_irv_convert_to_integer;
+        irv_convert_to_float = gen_irv_convert_to_float;
+        irv_convert_to_integer_nlt_type3 = gen_irv_convert_to_integer_nlt_type3;
+        irv_convert_to_float_nlt_type3 = gen_irv_convert_to_float_nlt_type3;
+        rct_forward = gen_rct_forward;
+        rct_backward = gen_rct_backward;
+        ict_forward = gen_ict_forward;
+        ict_backward = gen_ict_backward;
 
   #ifndef OJPH_DISABLE_SIMD
 
@@ -186,20 +183,19 @@ namespace ojph {
 
 #else // OJPH_ENABLE_WASM_SIMD
 
-      rev_convert = wasm_rev_convert;
-      rev_convert_nlt_type3 = wasm_rev_convert_nlt_type3;
-      irv_convert_to_integer = wasm_irv_convert_to_integer;
-      irv_convert_to_float = wasm_irv_convert_to_float;
-      irv_convert_to_integer_nlt_type3 = wasm_irv_convert_to_integer_nlt_type3;
-      irv_convert_to_float_nlt_type3 = wasm_irv_convert_to_float_nlt_type3;
-      rct_forward = wasm_rct_forward;
-      rct_backward = wasm_rct_backward;
-      ict_forward = wasm_ict_forward;
-      ict_backward = wasm_ict_backward;
+        rev_convert = wasm_rev_convert;
+        rev_convert_nlt_type3 = wasm_rev_convert_nlt_type3;
+        irv_convert_to_integer = wasm_irv_convert_to_integer;
+        irv_convert_to_float = wasm_irv_convert_to_float;
+        irv_convert_to_integer_nlt_type3 = wasm_irv_convert_to_integer_nlt_type3;
+        irv_convert_to_float_nlt_type3 = wasm_irv_convert_to_float_nlt_type3;
+        rct_forward = wasm_rct_forward;
+        rct_backward = wasm_rct_backward;
+        ict_forward = wasm_ict_forward;
+        ict_backward = wasm_ict_backward;
 
 #endif // !OJPH_ENABLE_WASM_SIMD
-
-      colour_transform_functions_initialized = true;
+      });
     }
 
     //////////////////////////////////////////////////////////////////////////
diff --git a/src/core/transform/ojph_transform.cpp b/src/core/transform/ojph_transform.cpp
index c4313ab..f67ea1b 100644
--- a/src/core/transform/ojph_transform.cpp
+++ b/src/core/transform/ojph_transform.cpp
@@ -36,6 +36,7 @@
 //***************************************************************************/
 
 #include <cstdio>
+#include <mutex>
 
 #include "ojph_arch.h"
 #include "ojph_mem.h"
@@ -93,25 +94,21 @@ namespace ojph {
       (const param_atk* atk, const line_buf* dst, const line_buf* lsrc,
         const line_buf* hsrc, ui32 width, bool even) = NULL;
 
-    ////////////////////////////////////////////////////////////////////////////
-    static bool wavelet_transform_functions_initialized = false;
-
     //////////////////////////////////////////////////////////////////////////
     void init_wavelet_transform_functions()
     {
-      if (wavelet_transform_functions_initialized)
-        return;
-
+      static std::once_flag wavelet_transform_functions_init_flag;
+      std::call_once(wavelet_transform_functions_init_flag, [](){
 #if !defined(OJPH_ENABLE_WASM_SIMD) || !defined(OJPH_EMSCRIPTEN)
 
-      rev_vert_step             = gen_rev_vert_step;
-      rev_horz_ana              = gen_rev_horz_ana;
-      rev_horz_syn              = gen_rev_horz_syn;
+        rev_vert_step             = gen_rev_vert_step;
+        rev_horz_ana              = gen_rev_horz_ana;
+        rev_horz_syn              = gen_rev_horz_syn;
 
-      irv_vert_step             = gen_irv_vert_step;
-      irv_vert_times_K          = gen_irv_vert_times_K;
-      irv_horz_ana              = gen_irv_horz_ana;
-      irv_horz_syn              = gen_irv_horz_syn;
+        irv_vert_step             = gen_irv_vert_step;
+        irv_vert_times_K          = gen_irv_vert_times_K;
+        irv_horz_ana              = gen_irv_horz_ana;
+        irv_horz_syn              = gen_irv_horz_syn;
 
   #ifndef OJPH_DISABLE_SIMD
 
@@ -185,8 +182,7 @@ namespace ojph {
         irv_horz_ana              = wasm_irv_horz_ana;
         irv_horz_syn              = wasm_irv_horz_syn;
 #endif // !OJPH_ENABLE_WASM_SIMD
-
-      wavelet_transform_functions_initialized = true;
+      });
     }
     
     //////////////////////////////////////////////////////////////////////////