diff --git a/TODO.md b/TODO.md
index a6c3bf2..4f1564b 100644
--- a/TODO.md
+++ b/TODO.md
@@ -15,7 +15,7 @@
 * [x] ~~~Delete Visual Studio 98 files~~~ - ✅;
 * [x] ~~~Delete Visual Studio 2003+ files~~~ - ✅;
 * [x] ~~~discriminate on `_WIN32` in implementation (and maybe also in API)~~~ - ✅;
-* [ ] check `CSTRING_USE_WINAPI_`;
+* [x] ~~~check `CSTRING_USE_WINAPI_`~~~;
 * [ ] custom arena(s);
 
 
diff --git a/src/cstring.core.c b/src/cstring.core.c
index b7668dd..b00bdec 100644
--- a/src/cstring.core.c
+++ b/src/cstring.core.c
@@ -59,7 +59,6 @@
 
 /* Standard C header files */
 
-#include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -78,13 +77,6 @@
 #define CSTRING_OFFSET_SIZE                                 (16)
 
 
-/* /////////////////////////////////////////////////////////////////////////
- * debugging
- */
-
-#define CSTRING_ASSERT(expr)                                assert(expr)
-
-
 /* /////////////////////////////////////////////////////////////////////////
  * character encoding
  */
@@ -302,7 +294,7 @@ cstring_realloc_2_(
 
             pvNew = realloc(pv, cb);
             break;
-#if defined(CSTRING_USE_WINAPI_)
+#ifdef _WIN32
         case    CSTRING_F_USE_WINDOWS_GLOBAL_MEMORY:
 
             pvNew = win32_global_realloc(pv, cb);
@@ -315,7 +307,7 @@ cstring_realloc_2_(
 
             pvNew = win32_comtask_realloc(pv, cb);
             break;
-#endif /* CSTRING_USE_WINAPI_ */
+#endif /* _WIN32 */
 #if defined(CSTRING_USE_SYNESIS_APIS)
         case    CSTRING_F_USE_SYNESIS_HATOR:
 #endif /* CSTRING_USE_SYNESIS_APIS */
diff --git a/src/cstring.vector.c b/src/cstring.vector.c
index 59152c8..81f43ed 100644
--- a/src/cstring.vector.c
+++ b/src/cstring.vector.c
@@ -51,6 +51,7 @@
 /* cstring header files */
 
 #include <cstring/cstring.vector.h>
+#include "internal.h"
 
 #ifndef CSTRING_INCL_CSTRING_INTERNAL_H_SAFESTR
 # include <cstring/internal/safestr.h>
@@ -58,7 +59,6 @@
 
 /* Standard C header files */
 
-#include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -114,7 +114,7 @@ cstring_vector_init(
 ,   size_t              minCapacity
 )
 {
-    CSTRING_VECTOR_ASSERT(NULL != pcsv);
+    CSTRING_ASSERT(NULL != pcsv);
 
     if (cstring_vector_DEFAULT_CAPACITY == minCapacity)
     {
@@ -158,7 +158,7 @@ cstring_vector_destroy(
     CSTRING_RC  rc = CSTRING_RC_SUCCESS;
     size_t      i;
 
-    CSTRING_VECTOR_ASSERT(NULL != pcsv);
+    CSTRING_ASSERT(NULL != pcsv);
 
     for (i = 0; i != pcsv->len; ++i)
     {
@@ -190,8 +190,8 @@ cstring_vector_truncate(
     CSTRING_RC  rc = CSTRING_RC_SUCCESS;
     size_t      i;
 
-    CSTRING_VECTOR_ASSERT(NULL != pcsv);
-    CSTRING_VECTOR_ASSERT(len <= pcsv->len);
+    CSTRING_ASSERT(NULL != pcsv);
+    CSTRING_ASSERT(len <= pcsv->len);
 
     for (i = len; i != pcsv->len; ++i)
     {
@@ -215,7 +215,7 @@ cstring_vector_create(
 ,   size_t              initialSize
 )
 {
-    CSTRING_VECTOR_ASSERT(NULL != pcsv);
+    CSTRING_ASSERT(NULL != pcsv);
 
     if (cstring_vector_DEFAULT_CAPACITY == initialSize)
     {
@@ -229,7 +229,7 @@ cstring_vector_create(
         {
             size_t i;
 
-            CSTRING_VECTOR_ASSERT(pcsv->capacity >= initialSize);
+            CSTRING_ASSERT(pcsv->capacity >= initialSize);
 
             for (i = 0; i != initialSize; ++i)
             {
@@ -272,8 +272,8 @@ cstring_vector_insertAt(
 ,   size_t              numStrings
 )
 {
-    CSTRING_VECTOR_ASSERT(NULL != pcsv);
-    CSTRING_VECTOR_ASSERT(NULL != strings || 0 == numStrings);
+    CSTRING_ASSERT(NULL != pcsv);
+    CSTRING_ASSERT(NULL != strings || 0 == numStrings);
 
     if (0 == numStrings)
     {
@@ -373,7 +373,7 @@ cstring_vector_readLines(
     size_t      numLinesRead_;
     size_t      initialLen;
 
-    CSTRING_VECTOR_ASSERT(NULL != pcsv);
+    CSTRING_ASSERT(NULL != pcsv);
 
     initialLen = pcsv->len;
 
diff --git a/src/dllmain.c b/src/dllmain.c
index 382b994..432a924 100644
--- a/src/dllmain.c
+++ b/src/dllmain.c
@@ -4,7 +4,7 @@
  * Purpose: Definition of DllMain for the Win32 platform
  *
  * Created: 19th August 2005
- * Updated: 2nd August 2026
+ * Updated: 29th September 2026
  *
  * Home:    http://synesis.com.au/software/
  *
@@ -49,6 +49,8 @@
  */
 
 #include <cstring/cstring.h>
+#include "internal.h"
+
 #if !defined(__MWERKS__)
 # include <windows.h>
 #else /* ? compiler */
diff --git a/src/internal.h b/src/internal.h
index c4f1c69..74cb2a4 100644
--- a/src/internal.h
+++ b/src/internal.h
@@ -48,29 +48,50 @@
 #define CSTRING_INCL_SRC_H_INTERNAL
 
 
+/* /////////////////////////////////////////////////////////////////////////
+ * checks
+ */
+
+#ifndef CSTRING_INCL_CSTRING_H_CSTRING
+# error cstring/cstring.h must be included before this file
+#endif /* !CSTRING_INCL_CSTRING_H_CSTRING */
+
+
 /* /////////////////////////////////////////////////////////////////////////
  * includes
  */
 
-#include <cstring/cstring.h>
+#include <assert.h>
 
 
 /* /////////////////////////////////////////////////////////////////////////
  * constants & definitions
  */
 
-#if defined(WIN32) || \
-    defined(WIN64)
 
-# define CSTRING_USE_WINAPI_
-#endif /* WIN32 || WIN64 */
+/* /////////////////////////////////////////////////////////////////////////
+ * macros
+ */
+
+
+/* /////////////////////////////////////////////////////////
+ * constract enforcements
+ */
+
+#define CSTRING_ASSERT(expr)                                assert(expr)
 
 
 /* /////////////////////////////////////////////////////////////////////////
+ * internal functions
+ */
+
+
+
+/* /////////////////////////////////////////////////////////
  * Windows arena allocators
  */
 
-#if defined(CSTRING_USE_WINAPI_)
+#ifdef _WIN32
 
 CSTRING_EXTERN_C
 void*
@@ -92,7 +113,7 @@ win32_comtask_realloc(
     void*   pv
 ,   size_t  cb
 );
-#endif /* CSTRING_USE_WINAPI_ */
+#endif /* _WIN32 */
 
 
 /* ////////////////////////////////////////////////////////////////////// */
diff --git a/src/win.c b/src/win.c
index 2490256..1d07a52 100644
--- a/src/win.c
+++ b/src/win.c
@@ -48,6 +48,7 @@
  * includes
  */
 
+#include <cstring/cstring.h>
 #include "internal.h"