diff --git a/generic/tcl.h b/generic/tcl.h
index 7ef41802877..f8a34c0043b 100644
--- a/generic/tcl.h
+++ b/generic/tcl.h
@@ -123,6 +123,7 @@ extern "C" {
  */
 
 #include <stdio.h>
+#include <stddef.h>
 
 /*
  *----------------------------------------------------------------------------
@@ -136,7 +137,7 @@ extern "C" {
  */
 
 #include <stdarg.h>
-#if !defined(TCL_NO_DEPRECATED) && TCL_MAJOR_VERSION < 9
+#ifndef TCL_NO_DEPRECATED
 #    define TCL_VARARGS(type, name) (type name, ...)
 #    define TCL_VARARGS_DEF(type, name) (type name, ...)
 #    define TCL_VARARGS_START(type, name, list) (va_start(list, name), name)
@@ -256,7 +257,7 @@ extern "C" {
  * New code should use prototypes.
  */
 
-#if !defined(TCL_NO_DEPRECATED) && TCL_MAJOR_VERSION < 9
+#ifndef TCL_NO_DEPRECATED
 #   undef _ANSI_ARGS_
 #   define _ANSI_ARGS_(x)	x
 
@@ -299,7 +300,7 @@ extern "C" {
  * VOID. This block is skipped under Cygwin and Mingw.
  */
 
-#if !defined(TCL_NO_DEPRECATED) && TCL_MAJOR_VERSION < 9
+#ifndef TCL_NO_DEPRECATED
 #if defined(_WIN32) && !defined(HAVE_WINNT_IGNORE_VOID)
 #ifndef VOID
 #define VOID void
@@ -317,7 +318,7 @@ typedef long LONG;
 #ifndef __VXWORKS__
 #   define VOID void
 #endif
-#endif /* !defined(TCL_NO_DEPRECATED) && TCL_MAJOR_VERSION < 9 */
+#endif /* !TCL_NO_DEPRECATED */
 
 /*
  * Miscellaneous declarations.
@@ -414,7 +415,6 @@ typedef unsigned TCL_WIDE_INT_TYPE	Tcl_WideUInt;
 #define Tcl_WideAsDouble(val)	((double)((Tcl_WideInt)(val)))
 #define Tcl_DoubleAsWide(val)	((Tcl_WideInt)((double)(val)))
 
-
 #if TCL_MAJOR_VERSION < 9
     typedef int Tcl_Size;
 #   define TCL_SIZE_MAX INT_MAX
@@ -476,7 +476,7 @@ typedef unsigned TCL_WIDE_INT_TYPE	Tcl_WideUInt;
  */
 
 typedef struct Tcl_Interp
-#if !defined(TCL_NO_DEPRECATED) && TCL_MAJOR_VERSION < 9
+#ifndef TCL_NO_DEPRECATED
 {
     /* TIP #330: Strongly discourage extensions from using the string
      * result. */
@@ -584,19 +584,28 @@ typedef void (Tcl_ThreadCreateProc) (void *clientData);
  */
 
 typedef struct Tcl_RegExpIndices {
-    long start;			/* Character offset of first character in
+#if TCL_MAJOR_VERSION > 8
+    Tcl_Size start;			/* Character offset of first character in
 				 * match. */
-    long end;			/* Character offset of first character after
+    Tcl_Size end;			/* Character offset of first character after
 				 * the match. */
+#else
+    long start;
+    long end;
+#endif
 } Tcl_RegExpIndices;
 
 typedef struct Tcl_RegExpInfo {
-    int nsubs;			/* Number of subexpressions in the compiled
+    Tcl_Size nsubs;			/* Number of subexpressions in the compiled
 				 * expression. */
     Tcl_RegExpIndices *matches;	/* Array of nsubs match offset pairs. */
-    long extendStart;		/* The offset at which a subsequent match
+#if TCL_MAJOR_VERSION > 8
+    Tcl_Size extendStart;		/* The offset at which a subsequent match
 				 * might begin. */
+#else
+    long extendStart;
     long reserved;		/* Reserved for later use. */
+#endif
 } Tcl_RegExpInfo;
 
 /*
@@ -634,7 +643,7 @@ typedef struct stat *Tcl_OldStat_;
 #define TCL_BREAK		3
 #define TCL_CONTINUE		4
 
-#if !defined(TCL_NO_DEPRECATED) && TCL_MAJOR_VERSION < 9
+#ifndef TCL_NO_DEPRECATED
 #define TCL_RESULT_SIZE		200
 #endif
 
@@ -652,7 +661,7 @@ typedef struct stat *Tcl_OldStat_;
  * Argument descriptors for math function callbacks in expressions:
  */
 
-#if !defined(TCL_NO_DEPRECATED) && TCL_MAJOR_VERSION < 9
+#ifndef TCL_NO_DEPRECATED
 typedef enum {
     TCL_INT, TCL_DOUBLE, TCL_EITHER, TCL_WIDE_INT
 } Tcl_ValueType;
@@ -696,7 +705,7 @@ typedef int (Tcl_CmdObjTraceProc) (void *clientData, Tcl_Interp *interp,
 	int level, const char *command, Tcl_Command commandInfo, int objc,
 	struct Tcl_Obj *const *objv);
 typedef int (Tcl_CmdObjTraceProc2) (void *clientData, Tcl_Interp *interp,
-	size_t level, const char *command, Tcl_Command commandInfo, size_t objc,
+	ptrdiff_t level, const char *command, Tcl_Command commandInfo, ptrdiff_t objc,
 	struct Tcl_Obj *const *objv);
 typedef void (Tcl_CmdObjTraceDeleteProc) (void *clientData);
 typedef void (Tcl_DupInternalRepProc) (struct Tcl_Obj *srcPtr,
@@ -723,7 +732,7 @@ typedef void (Tcl_NamespaceDeleteProc) (void *clientData);
 typedef int (Tcl_ObjCmdProc) (void *clientData, Tcl_Interp *interp,
 	int objc, struct Tcl_Obj *const *objv);
 typedef int (Tcl_ObjCmdProc2) (void *clientData, Tcl_Interp *interp,
-	size_t objc, struct Tcl_Obj *const *objv);
+	ptrdiff_t objc, struct Tcl_Obj *const *objv);
 typedef int (Tcl_LibraryInitProc) (Tcl_Interp *interp);
 typedef int (Tcl_LibraryUnloadProc) (Tcl_Interp *interp, int flags);
 typedef void (Tcl_PanicProc) (const char *format, ...);
@@ -972,9 +981,9 @@ typedef struct Tcl_DString {
 
 #define Tcl_DStringLength(dsPtr) ((dsPtr)->length)
 #define Tcl_DStringValue(dsPtr) ((dsPtr)->string)
-#if !defined(TCL_NO_DEPRECATED) && TCL_MAJOR_VERSION < 9
+#ifndef TCL_NO_DEPRECATED
 #   define Tcl_DStringTrunc Tcl_DStringSetLength
-#endif /* !TCL_NO_DEPRECATED */
+#endif
 
 /*
  * Definitions for the maximum number of digits of precision that may be
@@ -1096,7 +1105,7 @@ typedef struct Tcl_DString {
 #define TCL_TRACE_UNSETS	 0x40
 #define TCL_TRACE_DESTROYED	 0x80
 
-#if !defined(TCL_NO_DEPRECATED) && TCL_MAJOR_VERSION < 9
+#ifndef TCL_NO_DEPRECATED
 #define TCL_INTERP_DESTROYED	 0x100
 #endif
 
@@ -1134,9 +1143,9 @@ typedef struct Tcl_DString {
  * give the flag)
  */
 
-#if !defined(TCL_NO_DEPRECATED) && TCL_MAJOR_VERSION < 9
+#ifndef TCL_NO_DEPRECATED
 #   define TCL_PARSE_PART1	0x400
-#endif /* !TCL_NO_DEPRECATED */
+#endif
 
 /*
  * Types for linked variables:
@@ -1294,10 +1303,15 @@ struct Tcl_HashTable {
 				 * table. */
     Tcl_Size rebuildSize;		/* Enlarge table when numEntries gets to be
 				 * this large. */
+#if TCL_MAJOR_VERSION > 8
+    size_t mask;		/* Mask value used in hashing function. */
+#endif
     int downShift;		/* Shift count used in hashing function.
 				 * Designed to use high-order bits of
 				 * randomized keys. */
-    int mask;			/* Mask value used in hashing function. */
+#if TCL_MAJOR_VERSION < 9
+    int mask;		/* Mask value used in hashing function. */
+#endif
     int keyType;		/* Type of keys used in this table. It's
 				 * either TCL_CUSTOM_KEYS, TCL_STRING_KEYS,
 				 * TCL_ONE_WORD_KEYS, or an integer giving the
@@ -1463,7 +1477,11 @@ typedef void (Tcl_ScaleTimeProc) (Tcl_Time *timebuf, void *clientData);
  * interface.
  */
 
-#define TCL_CLOSE2PROC		((Tcl_DriverCloseProc *) 1)
+#if TCL_MAJOR_VERSION > 8
+#   define TCL_CLOSE2PROC		NULL
+#else
+#   define TCL_CLOSE2PROC		((Tcl_DriverCloseProc *)(void *)(size_t)1)
+#endif
 
 /*
  * Channel version tag. This was introduced in 8.3.2/8.4.
@@ -2038,6 +2056,12 @@ typedef struct Tcl_Parse {
 				 * *tokenPtr. */
     int errorType;		/* One of the parsing error types defined
 				 * above. */
+#if TCL_MAJOR_VERSION > 8
+    int incomplete;		/* This field is set to 1 by Tcl_ParseCommand
+				 * if the command appears to be incomplete.
+				 * This information is used by
+				 * Tcl_CommandComplete. */
+#endif
 
     /*
      * The fields below are intended only for the private use of the parser.
@@ -2056,10 +2080,9 @@ typedef struct Tcl_Parse {
 				 * beginning of region where the error
 				 * occurred (e.g. the open brace if the close
 				 * brace is missing). */
-    int incomplete;		/* This field is set to 1 by Tcl_ParseCommand
-				 * if the command appears to be incomplete.
-				 * This information is used by
-				 * Tcl_CommandComplete. */
+#if TCL_MAJOR_VERSION < 9
+    int incomplete;
+#endif
     Tcl_Token staticTokens[NUM_STATIC_TOKENS];
 				/* Initial space for tokens for command. This
 				 * space should be large enough to accommodate
@@ -2410,7 +2433,11 @@ typedef int (Tcl_NRPostProc) (void *data[], Tcl_Interp *interp,
  * stubs tables.
  */
 
-#define TCL_STUB_MAGIC		((int) 0xFCA3BACF)
+#if TCL_MAJOR_VERSION > 8
+#   define TCL_STUB_MAGIC		((int) 0xFCA3BACB + (int) sizeof(void *))
+#else
+#   define TCL_STUB_MAGIC		((int) 0xFCA3BACF)
+#endif
 
 /*
  * The following function is required to be defined in all stubs aware
@@ -2632,7 +2659,7 @@ EXTERN const char *TclZipfs_AppHook(int *argc, char ***argv);
  * Deprecated Tcl functions:
  */
 
-#if !defined(TCL_NO_DEPRECATED) && TCL_MAJOR_VERSION < 9
+#ifndef TCL_NO_DEPRECATED
 /*
  * These function have been renamed. The old names are deprecated, but we
  * define these macros for backwards compatibility.
diff --git a/generic/tclBasic.c b/generic/tclBasic.c
index 70d2160e154..4159cc467ec 100644
--- a/generic/tclBasic.c
+++ b/generic/tclBasic.c
@@ -9195,7 +9195,7 @@ Tcl_NRCallObjProc2(
     ptrdiff_t objc,
     Tcl_Obj *const objv[])
 {
-    if (objc > INT_MAX) {
+    if ((size_t)objc > INT_MAX) {
 	Tcl_WrongNumArgs(interp, 1, objv, "?args?");
 	return TCL_ERROR;
     }
diff --git a/generic/tclBinary.c b/generic/tclBinary.c
index 204830be80c..710ed0bf0c9 100644
--- a/generic/tclBinary.c
+++ b/generic/tclBinary.c
@@ -557,7 +557,7 @@ TclGetByteArrayFromObj(
 
     if (numBytesPtr != NULL) {
 	/* Make sure we return a value between 0 and UINT_MAX-1, or (size_t)-1 */
-	*numBytesPtr = ((size_t)(unsigned int)(baPtr->used + 1)) - 1;
+	*numBytesPtr = ((ptrdiff_t)(unsigned int)(baPtr->used + 1)) - 1;
     }
     return baPtr->bytes;
 }
diff --git a/generic/tclDecls.h b/generic/tclDecls.h
index 7d82250e827..9c3ca0d2550 100644
--- a/generic/tclDecls.h
+++ b/generic/tclDecls.h
@@ -4217,7 +4217,7 @@ extern const TclStubs *tclStubsPtr;
 #	define Tcl_SetPanicProc(arg) ((void)((Tcl_SetPanicProc)(arg)))
 #   endif
 #   define Tcl_MainEx Tcl_MainExW
-    EXTERN void Tcl_MainExW(int argc, wchar_t **argv,
+    EXTERN void Tcl_MainExW(Tcl_Size argc, wchar_t **argv,
 	    Tcl_AppInitProc *appInitProc, Tcl_Interp *interp);
 #elif !defined(TCL_NO_DEPRECATED)
 #   define Tcl_FindExecutable(arg) ((void)((Tcl_FindExecutable)(arg)))
diff --git a/generic/tclEncoding.c b/generic/tclEncoding.c
index db98d54129c..774485ddd25 100644
--- a/generic/tclEncoding.c
+++ b/generic/tclEncoding.c
@@ -602,7 +602,7 @@ TclInitEncodingSubsystem(void)
     type.nullSize	= 1;
     type.clientData	= INT2PTR(ENCODING_UTF);
     Tcl_CreateEncoding(&type);
-    type.clientData	= INT2PTR(0);
+    type.clientData	= NULL;
     type.encodingName	= "cesu-8";
     Tcl_CreateEncoding(&type);
 
@@ -614,7 +614,7 @@ TclInitEncodingSubsystem(void)
     type.clientData	= INT2PTR(TCL_ENCODING_LE);
     Tcl_CreateEncoding(&type);
     type.encodingName   = "ucs-2be";
-    type.clientData	= INT2PTR(0);
+    type.clientData	= NULL;
     Tcl_CreateEncoding(&type);
     type.encodingName   = "ucs-2";
     type.clientData	= INT2PTR(leFlags);
@@ -628,7 +628,7 @@ TclInitEncodingSubsystem(void)
     type.clientData	= INT2PTR(TCL_ENCODING_LE);
     Tcl_CreateEncoding(&type);
     type.encodingName   = "utf-32be";
-    type.clientData	= INT2PTR(0);
+    type.clientData	= NULL;
     Tcl_CreateEncoding(&type);
     type.encodingName   = "utf-32";
     type.clientData	= INT2PTR(leFlags);
@@ -639,13 +639,13 @@ TclInitEncodingSubsystem(void)
     type.freeProc	= NULL;
     type.nullSize	= 2;
     type.encodingName   = "utf-16le";
-    type.clientData	= INT2PTR(TCL_ENCODING_LE|ENCODING_UTF);
+    type.clientData	= INT2PTR(TCL_ENCODING_LE);
     Tcl_CreateEncoding(&type);
     type.encodingName   = "utf-16be";
-    type.clientData	= INT2PTR(ENCODING_UTF);
+    type.clientData	= NULL;
     Tcl_CreateEncoding(&type);
     type.encodingName   = "utf-16";
-    type.clientData	= INT2PTR(leFlags|ENCODING_UTF);
+    type.clientData	= INT2PTR(leFlags);
     Tcl_CreateEncoding(&type);
 
 #ifndef TCL_NO_DEPRECATED
diff --git a/generic/tclOO.h b/generic/tclOO.h
index 6f1849160a6..775bd32f44a 100644
--- a/generic/tclOO.h
+++ b/generic/tclOO.h
@@ -63,7 +63,7 @@ typedef struct Tcl_ObjectContext_ *Tcl_ObjectContext;
 typedef int (Tcl_MethodCallProc)(void *clientData, Tcl_Interp *interp,
 	Tcl_ObjectContext objectContext, int objc, Tcl_Obj *const *objv);
 typedef int (Tcl_MethodCallProc2)(void *clientData, Tcl_Interp *interp,
-	Tcl_ObjectContext objectContext, size_t objc, Tcl_Obj *const *objv);
+	Tcl_ObjectContext objectContext, ptrdiff_t objc, Tcl_Obj *const *objv);
 typedef void (Tcl_MethodDeleteProc)(void *clientData);
 typedef int (Tcl_CloneProc)(Tcl_Interp *interp, void *oldClientData,
 	void **newClientData);
diff --git a/generic/tclObj.c b/generic/tclObj.c
index aeaa0cd6dd9..93e3a08929c 100644
--- a/generic/tclObj.c
+++ b/generic/tclObj.c
@@ -1751,11 +1751,7 @@ TclGetStringFromObj(
 	}
     }
     if (lengthPtr != NULL) {
-#if TCL_MAJOR_VERSION > 8
-	*lengthPtr = objPtr->length;
-#else
-	*lengthPtr = ((size_t)(unsigned)(objPtr->length + 1)) - 1;
-#endif
+	*lengthPtr = ((ptrdiff_t)(unsigned)(objPtr->length + 1)) - 1;
     }
     return objPtr->bytes;
 }
@@ -4081,7 +4077,7 @@ Tcl_GetNumber(
 	numBytes = 0;
     }
     if (numBytes < 0) {
-	numBytes = strlen(bytes);
+	numBytes = (ptrdiff_t)strlen(bytes);
     }
     if (numBytes > INT_MAX) {
 	if (interp) {
diff --git a/generic/tclProc.c b/generic/tclProc.c
index d02cac24125..3abf3c39519 100644
--- a/generic/tclProc.c
+++ b/generic/tclProc.c
@@ -1690,7 +1690,7 @@ NRInterpProc2(
 				 * interpreted. */
     Tcl_Interp *interp,/* Interpreter in which procedure was
 				 * invoked. */
-    size_t objc,			/* Count of number of arguments to this
+    ptrdiff_t objc,			/* Count of number of arguments to this
 				 * procedure. */
     Tcl_Obj *const objv[])	/* Argument value objects. */
 {
@@ -1709,7 +1709,7 @@ ObjInterpProc2(
 				 * interpreted. */
     Tcl_Interp *interp,/* Interpreter in which procedure was
 				 * invoked. */
-    size_t objc,			/* Count of number of arguments to this
+    ptrdiff_t objc,			/* Count of number of arguments to this
 				 * procedure. */
     Tcl_Obj *const objv[])	/* Argument value objects. */
 {
diff --git a/generic/tclStubInit.c b/generic/tclStubInit.c
index 3a51f7eeada..104375e81e8 100644
--- a/generic/tclStubInit.c
+++ b/generic/tclStubInit.c
@@ -97,7 +97,7 @@ static void uniCodePanic(void) {
 }
 #   define Tcl_GetUnicode (unsigned short *(*)(Tcl_Obj *))(void *)uniCodePanic
 #   define Tcl_GetUnicodeFromObj (unsigned short *(*)(Tcl_Obj *, int *))(void *)uniCodePanic
-#   define TclGetUnicodeFromObj (unsigned short *(*)(Tcl_Obj *, size_t *))(void *)uniCodePanic
+#   define TclGetUnicodeFromObj (unsigned short *(*)(Tcl_Obj *, ptrdiff_t *))(void *)uniCodePanic
 #   define Tcl_NewUnicodeObj (Tcl_Obj *(*)(const unsigned short *, int))(void *)uniCodePanic
 #   define Tcl_SetUnicodeObj (void(*)(Tcl_Obj *, const unsigned short *, int))(void *)uniCodePanic
 #   define Tcl_AppendUnicodeToObj (void(*)(Tcl_Obj *, const unsigned short *, int))(void *)uniCodePanic
diff --git a/tests/ioCmd.test b/tests/ioCmd.test
index 2a1f6165e3e..e132b9ac6a3 100644
--- a/tests/ioCmd.test
+++ b/tests/ioCmd.test
@@ -1072,7 +1072,7 @@ test iocmd-23.1 {chan read, regular data return} -match glob -body {
     rename foo {}
     set res
 } -result {{read rc* 4096} {read rc* 4096} snarfsnarf}
-test iocmd-23.2 {chan read, bad data return, to much} -match glob -body {
+test iocmd-23.2 {chan read, bad data return, too much} -match glob -body {
     set res {}
     proc foo {args} {
 	oninit; onfinal; track
@@ -2383,7 +2383,7 @@ test iocmd.tf-23.1 {chan read, regular data return} -match glob -body {
     rename foo {}
     set res
 } -constraints {testchannel thread} -result {{read rc* 4096} {read rc* 4096} snarfsnarf}
-test iocmd.tf-23.2 {chan read, bad data return, to much} -match glob -body {
+test iocmd.tf-23.2 {chan read, bad data return, too much} -match glob -body {
     set res {}
     proc foo {args} {
 	oninit; onfinal; track
diff --git a/tools/regexpTestLib.tcl b/tools/regexpTestLib.tcl
index 454a4e88524..71dc9093077 100644
--- a/tools/regexpTestLib.tcl
+++ b/tools/regexpTestLib.tcl
@@ -42,7 +42,7 @@ proc readInputFile {} {
 
 #
 # strings with embedded @'s are truncated
-# unpreceeded @'s are replaced by {}
+# unpreceded @'s are replaced by {}
 #
 proc removeAts {ls} {
     set len [llength $ls]
diff --git a/unix/dltest/pkgt.c b/unix/dltest/pkgt.c
index e8047db98be..0c4b3d7089f 100644
--- a/unix/dltest/pkgt.c
+++ b/unix/dltest/pkgt.c
@@ -16,10 +16,10 @@
 static int TraceProc2 (
     void *clientData,
     Tcl_Interp *interp,
-    size_t level,
+    ptrdiff_t level,
     const char *command,
     Tcl_Command commandInfo,
-    size_t objc,
+    ptrdiff_t objc,
     struct Tcl_Obj *const *objv)
 {
     (void)clientData;
@@ -55,12 +55,12 @@ static int
 Pkgt_EqObjCmd2(
     void *dummy,		/* Not used. */
     Tcl_Interp *interp,		/* Current interpreter. */
-    size_t objc,			/* Number of arguments. */
+    ptrdiff_t objc,			/* Number of arguments. */
     Tcl_Obj *const objv[])	/* Argument objects. */
 {
     Tcl_WideInt result;
     const char *str1, *str2;
-    size_t len1, len2;
+    ptrdiff_t len1, len2;
     (void)dummy;
 
     if (objc != 3) {
@@ -71,7 +71,7 @@ Pkgt_EqObjCmd2(
     str1 = Tcl_GetStringFromObj(objv[1], &len1);
     str2 = Tcl_GetStringFromObj(objv[2], &len2);
     if (len1 == len2) {
-	result = (Tcl_UtfNcmp(str1, str2, len1) == 0);
+	result = (Tcl_UtfNcmp(str1, str2, (size_t)len1) == 0);
     } else {
 	result = 0;
     }
diff --git a/win/tclAppInit.c b/win/tclAppInit.c
index 27eb1641d11..a3914f131d5 100644
--- a/win/tclAppInit.c
+++ b/win/tclAppInit.c
@@ -141,7 +141,7 @@ _tmain(
     TclZipfs_AppHook(&argc, &argv);
 #endif
 
-    Tcl_Main((size_t)argc, argv, TCL_LOCAL_APPINIT);
+    Tcl_Main(argc, argv, TCL_LOCAL_APPINIT);
     return 0;			/* Needed only to prevent compiler warning. */
 }