diff --git a/generic/ttk/ttkTheme.c b/generic/ttk/ttkTheme.c
index 730de5d8d..ecb62fa17 100644
--- a/generic/ttk/ttkTheme.c
+++ b/generic/ttk/ttkTheme.c
@@ -95,7 +95,7 @@ Tcl_Obj *Ttk_StyleMap(Ttk_Style style, const char *optionName, Ttk_State state)
 
 /*
  * Ttk_StyleDefault --
- * 	Look up default resource setting the in the specified style.
+ * 	Look up default resource setting in the specified style.
  */
 Tcl_Obj *Ttk_StyleDefault(Ttk_Style style, const char *optionName)
 {
@@ -216,7 +216,7 @@ GetOptionMap(Ttk_ElementClass *elementClass, Tk_OptionTable optionTable)
  * 	from the specified element specification.
  */
 static Ttk_ElementClass *
-NewElementClass(const char *name, Ttk_ElementSpec *specPtr,void *clientData)
+NewElementClass(const char *name, Ttk_ElementSpec *specPtr, void *clientData)
 {
     Ttk_ElementClass *elementClass = (Ttk_ElementClass *)ckalloc(sizeof(Ttk_ElementClass));
     int i;
@@ -237,7 +237,7 @@ NewElementClass(const char *name, Ttk_ElementSpec *specPtr,void *clientData)
     elementClass->defaultValues = (Tcl_Obj **)
 	ckalloc(elementClass->nResources * sizeof(Tcl_Obj *) + 1);
     for (i=0; i < elementClass->nResources; ++i) {
-        const char *defaultValue = specPtr->options[i].defaultValue;
+	const char *defaultValue = specPtr->options[i].defaultValue;
 	if (defaultValue) {
 	    elementClass->defaultValues[i] = Tcl_NewStringObj(defaultValue,-1);
 	    Tcl_IncrRefCount(elementClass->defaultValues[i]);
@@ -407,7 +407,7 @@ typedef struct
  *	Cleanup procedure for StylePackageData.
  */
 static void Ttk_StylePkgFree(
-    ClientData clientData,
+    void *clientData,
     TCL_UNUSED(Tcl_Interp *))
 {
     StylePackageData *pkgPtr = (StylePackageData *)clientData;
@@ -475,7 +475,7 @@ static StylePackageData *GetStylePackageData(Tcl_Interp *interp)
  *
  */
 void Ttk_RegisterCleanup(
-    Tcl_Interp *interp, ClientData clientData, Ttk_CleanupProc *cleanupProc)
+    Tcl_Interp *interp, void *clientData, Ttk_CleanupProc *cleanupProc)
 {
     StylePackageData *pkgPtr = GetStylePackageData(interp);
     Cleanup *cleanup = (Cleanup *)ckalloc(sizeof(*cleanup));
@@ -498,7 +498,7 @@ void Ttk_RegisterCleanup(
  * 	the widget hierarchy, so this is done by evaluating a Tcl script.
  */
 
-static void ThemeChangedProc(ClientData clientData)
+static void ThemeChangedProc(void *clientData)
 {
     static char ThemeChangedScript[] = "ttk::ThemeChanged";
     StylePackageData *pkgPtr = (StylePackageData *)clientData;
@@ -534,9 +534,10 @@ void Ttk_TkDestroyedHandler(
     StylePackageData* pkgPtr = GetStylePackageData(interp);
 
     /*
-     * Cancel any pending ThemeChanged calls:
+     * Cancel any pending ThemeChanged calls. We might be called
+     * before Ttk is initialized. See bug [3981091ed336].
      */
-    if (pkgPtr->themeChangePending) {
+    if (pkgPtr && pkgPtr->themeChangePending) {
 	Tcl_CancelIdleCall(ThemeChangedProc, pkgPtr);
     }
 }
@@ -1188,7 +1189,7 @@ static Tcl_Obj* HashTableToDict(Tcl_HashTable *ht)
  */
 static int
 StyleMapCmd(
-    ClientData clientData,		/* StylePackageData pointer */
+    void *clientData,		/* StylePackageData pointer */
     Tcl_Interp *interp,			/* Current interpreter */
     int objc,				/* Number of arguments */
     Tcl_Obj *const objv[])		/* Argument objects */
@@ -1255,7 +1256,7 @@ StyleMapCmd(
 /* + style configure $style -option ?value...
  */
 static int StyleConfigureCmd(
-    ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
+    void *clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
 {
     StylePackageData *pkgPtr = (StylePackageData *)clientData;
     Ttk_Theme theme = pkgPtr->currentTheme;
@@ -1272,10 +1273,10 @@ static int StyleConfigureCmd(
     styleName = Tcl_GetString(objv[2]);
     stylePtr = Ttk_GetStyle(theme, styleName);
 
-    if (objc == 3) {		/* style default $styleName */
+    if (objc == 3) {		/* style configure $styleName */
 	Tcl_SetObjResult(interp, HashTableToDict(&stylePtr->defaultsTable));
 	return TCL_OK;
-    } else if (objc == 4) {	/* style default $styleName -option */
+    } else if (objc == 4) {	/* style configure $styleName -option */
 	const char *optionName = Tcl_GetString(objv[3]);
 	Tcl_HashEntry *entryPtr =
 	    Tcl_FindHashEntry(&stylePtr->defaultsTable, optionName);
@@ -1310,7 +1311,7 @@ static int StyleConfigureCmd(
 /* + style lookup $style -option ?statespec? ?defaultValue?
  */
 static int StyleLookupCmd(
-    ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
+    void *clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
 {
     StylePackageData *pkgPtr = (StylePackageData *)clientData;
     Ttk_Theme theme = pkgPtr->currentTheme;
@@ -1352,7 +1353,7 @@ static int StyleLookupCmd(
 }
 
 static int StyleThemeCurrentCmd(
-    ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj * const objv[])
+    void *clientData, Tcl_Interp *interp, int objc, Tcl_Obj * const objv[])
 {
     StylePackageData *pkgPtr = (StylePackageData *)clientData;
     Tcl_HashSearch search;
@@ -1388,7 +1389,7 @@ static int StyleThemeCurrentCmd(
 /* + style theme create name ?-parent $theme? ?-settings { script }?
  */
 static int StyleThemeCreateCmd(
-    ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
+    void *clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
 {
     StylePackageData *pkgPtr = (StylePackageData *)clientData;
     static const char *const optStrings[] =
@@ -1452,10 +1453,10 @@ static int StyleThemeCreateCmd(
  * 	Return list of registered themes.
  */
 static int StyleThemeNamesCmd(
-    ClientData clientData,
+    void *clientData,
     Tcl_Interp *interp,
-    TCL_UNUSED(int),
-    TCL_UNUSED(Tcl_Obj *const *))
+    TCL_UNUSED(int), /* objc */
+    TCL_UNUSED(Tcl_Obj *const *)) /* objv */
 {
     StylePackageData *pkgPtr = (StylePackageData *)clientData;
 
@@ -1469,7 +1470,7 @@ static int StyleThemeNamesCmd(
  */
 static int
 StyleThemeSettingsCmd(
-    ClientData clientData,		/* StylePackageData pointer */
+    void *clientData,		/* StylePackageData pointer */
     Tcl_Interp *interp,			/* Current interpreter */
     int objc,				/* Number of arguments */
     Tcl_Obj *const objv[])		/* Argument objects */
@@ -1498,7 +1499,7 @@ StyleThemeSettingsCmd(
 /* + style element create name type ? ...args ?
  */
 static int StyleElementCreateCmd(
-    ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
+    void *clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
 {
     StylePackageData *pkgPtr = (StylePackageData *)clientData;
     Ttk_Theme theme = pkgPtr->currentTheme;
@@ -1533,7 +1534,7 @@ static int StyleElementCreateCmd(
  * 	Return a list of elements defined in the current theme.
  */
 static int StyleElementNamesCmd(
-    ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
+    void *clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
 {
     StylePackageData *pkgPtr = (StylePackageData *)clientData;
     Ttk_Theme theme = pkgPtr->currentTheme;
@@ -1549,7 +1550,7 @@ static int StyleElementNamesCmd(
  * 	Return list of element options for specified element
  */
 static int StyleElementOptionsCmd(
-    ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
+    void *clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
 {
     StylePackageData *pkgPtr = (StylePackageData *)clientData;
     Ttk_Theme theme = pkgPtr->currentTheme;
@@ -1587,7 +1588,7 @@ static int StyleElementOptionsCmd(
 /* + style layout name ?spec?
  */
 static int StyleLayoutCmd(
-    ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
+    void *clientData, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
 {
     StylePackageData *pkgPtr = (StylePackageData *)clientData;
     Ttk_Theme theme = pkgPtr->currentTheme;
@@ -1627,7 +1628,7 @@ static int StyleLayoutCmd(
  */
 static int
 StyleThemeUseCmd(
-    ClientData clientData,		/* StylePackageData pointer */
+    void *clientData,		/* StylePackageData pointer */
     Tcl_Interp *interp,			/* Current interpreter */
     int objc,				/* Number of arguments */
     Tcl_Obj *const objv[])		/* Argument objects */
@@ -1684,7 +1685,7 @@ static const Ttk_Ensemble StyleEnsemble[] = {
 
 static int
 StyleObjCmd(
-    ClientData clientData,		/* StylePackageData pointer */
+    void *clientData,		/* StylePackageData pointer */
     Tcl_Interp *interp,			/* Current interpreter */
     int objc,				/* Number of arguments */
     Tcl_Obj *const objv[])		/* Argument objects */