diff --git a/Makefile b/Makefile
index bc518bf..779ae11 100644
--- a/Makefile
+++ b/Makefile
@@ -282,9 +282,13 @@ preview-man: man
 test: DEBUGFLAGS += -DDEBUGLEVEL=1
 test: all namespaceTest check test-xxhsum-c c90test test-tools
 
+.PHONY: test-inline
+test-inline:
+	$(MAKE) -C tests test
+
 .PHONY: test-all
 test-all: CFLAGS += -Werror
-test-all: test test32 clangtest cxxtest usan listL120 trailingWhitespace staticAnalyze
+test-all: test test32 clangtest cxxtest usan test-inline listL120 trailingWhitespace staticAnalyze
 
 .PHONY: test-tools
 test-tools:
diff --git a/tests/Makefile b/tests/Makefile
new file mode 100644
index 0000000..2e4d7de
--- /dev/null
+++ b/tests/Makefile
@@ -0,0 +1,45 @@
+CFLAGS += -Wall -Wextra -g
+
+NM = nm
+GREP = grep
+
+.PHONY: default
+default: all
+
+.PHONY: all
+all: test
+
+.PHONY: test
+test: test_multiinclude
+
+.PHONY: test_multiinclude
+test_multiinclude:
+	@$(MAKE) clean
+	# compile without xxhash.o, ensure symbols exist within target
+	# note : built using only default rules
+	$(MAKE) multiInclude
+	@$(MAKE) clean
+	# compile with xxhash.o, to detect duplicated symbols
+	$(MAKE) multiInclude_withxxhash
+	@$(MAKE) clean
+	# Note : XXH_INLINE_ALL with XXH_NAMESPACE is currently disabled
+	# compile with XXH_NAMESPACE
+	# CPPFLAGS=-DXXH_NAMESPACE=TESTN_ $(MAKE) multiInclude_withxxhash
+	# no symbol prefixed TESTN_ should exist
+	# ! $(NM) multiInclude_withxxhash | $(GREP) TESTN_
+	#$(MAKE) clean
+	# compile with XXH_NAMESPACE and without xxhash.o
+	# CPPFLAGS=-DXXH_NAMESPACE=TESTN_ $(MAKE) multiInclude
+	# no symbol prefixed TESTN_ should exist
+	# ! $(NM) multiInclude | $(GREP) TESTN_
+	#@$(MAKE) clean
+
+xxhash.o: ../xxhash.c ../xxhash.h
+	$(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS) -c -o $@ $<
+
+multiInclude_withxxhash: multiInclude.o xxhash.o
+	$(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS) -o $@ $^
+
+clean:
+	@$(RM) *.o
+	@$(RM) multiInclude multiInclude_withxxhash
diff --git a/tests/multiInclude.c b/tests/multiInclude.c
new file mode 100644
index 0000000..7a81305
--- /dev/null
+++ b/tests/multiInclude.c
@@ -0,0 +1,58 @@
+/*
+*  test_multiinclude
+*  test program, just to validate including multiple times in any order
+*
+*  Copyright (C) Yann Collet 2013-present
+*
+*  GPL v2 License
+*
+*  This program is free software; you can redistribute it and/or modify
+*  it under the terms of the GNU General Public License as published by
+*  the Free Software Foundation; either version 2 of the License, or
+*  (at your option) any later version.
+*
+*  This program is distributed in the hope that it will be useful,
+*  but WITHOUT ANY WARRANTY; without even the implied warranty of
+*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*  GNU General Public License for more details.
+*
+*  You should have received a copy of the GNU General Public License along
+*  with this program; if not, write to the Free Software Foundation, Inc.,
+*  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*
+*  You can contact the author at :
+*  - xxHash homepage : http://www.xxhash.com
+*  - xxHash source repository : https://github.com/Cyan4973/xxHash
+*/
+
+#include <stdio.h>  // printf
+
+/* normal include, gives access to public symbols */
+#include "../xxhash.h"
+
+/* advanced include, gives access to experimental symbols */
+/* note : without specific effort, experimental symbols might be unavailable */
+#define XXH_STATIC_LINKING_ONLY
+#include "../xxhash.h"
+
+/* inlining : re-define all symbols, keep them private to the unit.
+ * note : without specific efforts, symbol names will collide
+ * note 2 : no linking to xxhash.o, so that link stage will fail if inline is ignored */
+#define XXH_INLINE_ALL
+#include "../xxhash.h"
+
+
+int main(void)
+{
+    XXH3_state_t state;   /* part of experimental */
+
+    XXH3_64bits_reset(&state);
+    const char input[] = "Hello World !";
+
+    XXH3_64bits_update(&state, input, sizeof(input));
+
+    XXH64_hash_t const h = XXH3_64bits_digest(&state);
+    printf("hash '%s' : %0llx \n", input, (unsigned long long)h);
+
+    return 0;
+}
diff --git a/xxh3.h b/xxh3.h
index 8961d71..1f0592c 100644
--- a/xxh3.h
+++ b/xxh3.h
@@ -1654,7 +1654,7 @@ XXH_PUBLIC_API XXH128_hash_t XXH3_128bits_digest (const XXH3_state_t* state)
 
 /* 128-bit utility functions */
 
-#include <string.h>   /* memcmp */
+#include <string.h>   /* memcmp, memcpy */
 
 /* return : 1 is equal, 0 if different */
 XXH_PUBLIC_API int XXH128_isEqual(XXH128_hash_t h1, XXH128_hash_t h2)
diff --git a/xxhash.c b/xxhash.c
index a17d836..80631eb 100644
--- a/xxhash.c
+++ b/xxhash.c
@@ -33,7 +33,7 @@
 */
 
 
-/* xxhash.c only instantiates functions defined in xxhash.h
+/* xxhash.c instantiates functions defined in xxhash.h
  */
 
 #define XXH_STATIC_LINKING_ONLY   /* access advanced declarations */
diff --git a/xxhash.h b/xxhash.h
index a2323c3..988ee33 100644
--- a/xxhash.h
+++ b/xxhash.h
@@ -73,29 +73,29 @@ XXH32        6.8 GB/s            6.0 GB/s
 extern "C" {
 #endif
 
-
-#ifndef XXHASH_H_5627135585666179
-#define XXHASH_H_5627135585666179 1
-
 /* ****************************
  *  API modifier
  ******************************/
 /** XXH_INLINE_ALL (and XXH_PRIVATE_API)
- *  This build macro includes xxhash functions in `static` mode
- *  in order to inline them, and remove their symbol from the public list.
- *  Inlining offers great performance improvement on small keys,
+ *  Implement requested xxhash functions directly in the unit.
+ *  Inlining offers great performance improvement on small inputs,
  *  and dramatic ones when length is expressed as a compile-time constant.
  *  See https://fastcompression.blogspot.com/2018/03/xxhash-for-small-keys-impressive-power.html .
+ *  It also removes all symbols from the public list.
  *  Methodology :
  *     #define XXH_INLINE_ALL
  *     #include "xxhash.h"
- * `xxhash.c` is automatically included.
- *  It's not useful to compile and link it as a separate object.
+ *  Do not compile and link xxhash.o as a separate object (not useful)
  */
-#if defined(XXH_INLINE_ALL) || defined(XXH_PRIVATE_API)
-#  ifndef XXH_STATIC_LINKING_ONLY
-#    define XXH_STATIC_LINKING_ONLY
-#  endif
+#if (defined(XXH_INLINE_ALL) || defined(XXH_PRIVATE_API)) \
+    && !defined(XXH_INLINE_ALL_31684351384)
+   /* this section should be traversed only once */
+#  define XXH_INLINE_ALL_31684351384
+   /* give access to advanced API, required to compile implementations */
+#  undef XXH_STATIC_LINKING_ONLY   /* avoid macro redef */
+#  define XXH_STATIC_LINKING_ONLY
+   /* make functions private */
+#  undef XXH_PUBLIC_API
 #  if defined(__GNUC__)
 #    define XXH_PUBLIC_API static __inline __attribute__((unused))
 #  elif defined (__cplusplus) || (defined (__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L) /* C99 */)
@@ -103,10 +103,48 @@ extern "C" {
 #  elif defined(_MSC_VER)
 #    define XXH_PUBLIC_API static __inline
 #  else
-     /* this version may generate warnings for unused static functions */
+     /* note : this version may generate warnings for unused static functions */
 #    define XXH_PUBLIC_API static
 #  endif
-#else
+
+   /* prefix all names, to avoid symbol duplicates with potential library */
+#  ifdef XXH_NAMESPACE
+#    error "XXH_INLINE_ALL with XXH_NAMESPACE is not supported"
+#    /* Note : Alternative is to #undef all symbols (it's a pretty large list).
+      * If doing nothing : it compiles, but functions are actually Not inlined.
+      * */
+#  endif
+#  define XXH_NAMESPACE XXH_INLINE_
+   /* some identifiers are not symbols,
+    * they must nonetheless be renamed to avoid double declaration
+    * Alternative : do not redeclare them,
+    * which requires some #ifdef, and is more dispersed in the file
+    * while renaming can be achieved in a single place */
+#  define XXH_IPREF(Id)   XXH_INLINE_ ## Id
+#  define XXH_OK XXH_IPREF(XXH_OK)
+#  define XXH_ERROR XXH_IPREF(XXH_ERROR)
+#  define XXH_errorcode XXH_IPREF(XXH_errorcode)
+#  define XXH32_canonical_t XXH_IPREF(XXH32_canonical_t)
+#  define XXH64_canonical_t XXH_IPREF(XXH64_canonical_t)
+#  define XXH128_canonical_t XXH_IPREF(XXH128_canonical_t)
+#  define XXH32_state_s XXH_IPREF(XXH32_state_s)
+#  define XXH32_state_t XXH_IPREF(XXH32_state_t)
+#  define XXH64_state_s XXH_IPREF(XXH64_state_s)
+#  define XXH64_state_t XXH_IPREF(XXH64_state_t)
+#  define XXH3_state_s XXH_IPREF(XXH3_state_s)
+#  define XXH3_state_t XXH_IPREF(XXH3_state_t)
+#  define XXH128_hash_t XXH_IPREF(XXH128_hash_t)
+   /* Ensure header is parsed again, even if it was previously included */
+#  undef XXHASH_H_5627135585666179
+#  undef XXHASH_H_STATIC_13879238742
+#endif /* XXH_INLINE_ALL || XXH_PRIVATE_API */
+
+
+#ifndef XXHASH_H_5627135585666179
+#define XXHASH_H_5627135585666179 1
+
+/* specific declaration modes for Windows */
+#if !defined(XXH_INLINE_ALL) && !defined(XXH_PRIVATE_API)
 #  if defined(WIN32) && defined(_MSC_VER) && (defined(XXH_IMPORT) || defined(XXH_EXPORT))
 #    ifdef XXH_EXPORT
 #      define XXH_PUBLIC_API __declspec(dllexport)
@@ -116,7 +154,7 @@ extern "C" {
 #  else
 #    define XXH_PUBLIC_API   /* do nothing */
 #  endif
-#endif /* XXH_INLINE_ALL || XXH_PRIVATE_API */
+#endif
 
 /*! XXH_NAMESPACE, aka Namespace Emulation :
  *
@@ -577,9 +615,14 @@ XXH_PUBLIC_API XXH128_hash_t XXH128_hashFromCanonical(const XXH128_canonical_t*
 #endif  /* defined(XXH_STATIC_LINKING_ONLY) && !defined(XXHASH_H_STATIC_13879238742) */
 
 
+/* ======================================================================== */
+/* ======================================================================== */
+/* ======================================================================== */
+
 
 /*-**********************************************************************
 *  xxHash implementation
+* -**********************************************************************
 *  Functions implementation used to be hosted within xxhash.c .
 *  However, code inlining requires to place implementation in the header file.
 *  As a consequence, xxhash.c used to be included within xxhash.h .