Index: generic/tclStringObj.c
==================================================================
--- generic/tclStringObj.c
+++ generic/tclStringObj.c
@@ -67,19 +67,10 @@
 static void		SetUnicodeObj(Tcl_Obj *objPtr,
 			    const Tcl_UniChar *unicode, Tcl_Size numChars);
 static Tcl_Size		UnicodeLength(const Tcl_UniChar *unicode);
 static void		UpdateStringOfString(Tcl_Obj *objPtr);
 
-#if TCL_UTF_MAX > 3
-#define ISCONTINUATION(bytes) (\
-	((bytes)[0] & 0xC0) == 0x80)
-#else
-#define ISCONTINUATION(bytes) (\
-	((((bytes)[0] & 0xC0) == 0x80) || (((bytes)[0] == '\xED') \
-	&& (((bytes)[1] & 0xF0) == 0xB0) && (((bytes)[2] & 0xC0) == 0x80))))
-#endif
-
 
 /*
  * The structure below defines the string Tcl object type by means of
  * functions that can be invoked by generic object code.
  */
@@ -1300,16 +1291,10 @@
     }
 
     SetStringFromAny(NULL, objPtr);
     stringPtr = GET_STRING(objPtr);
 
-    /* If appended string starts with a continuation byte or a lower surrogate,
-     * force objPtr to unicode representation. See [7f1162a867] */
-    if (bytes && ISCONTINUATION(bytes)) {
-	Tcl_GetUnicode(objPtr);
-	stringPtr = GET_STRING(objPtr);
-    }
     if (stringPtr->hasUnicode && (stringPtr->numChars+1) > 1) {
 	AppendUtfToUnicodeRep(objPtr, bytes, toCopy);
     } else {
 	AppendUtfToUtfRep(objPtr, bytes, toCopy);
     }
@@ -1505,17 +1490,10 @@
      */
 
     SetStringFromAny(NULL, objPtr);
     stringPtr = GET_STRING(objPtr);
 
-    /* If appended string starts with a continuation byte or a lower surrogate,
-     * force objPtr to unicode representation. See [7f1162a867]
-     * This fixes append-3.4, append-3.7 and utf-1.18 testcases. */
-    if (ISCONTINUATION(TclGetString(appendObjPtr))) {
-	Tcl_GetUnicode(objPtr);
-	stringPtr = GET_STRING(objPtr);
-    }
     /*
      * If objPtr has a valid Unicode rep, then get a Unicode string from
      * appendObjPtr and append it.
      */
 
@@ -3175,13 +3153,11 @@
 		 * Non-empty string rep. Not a pure bytearray, so we won't
 		 * create a pure bytearray.
 		 */
 
 	 	binary = 0;
-	 	if (ov > objv+1 && ISCONTINUATION(TclGetString(objPtr))) {
-	 	    forceUniChar = 1;
-	 	} else if ((objPtr->typePtr) && (objPtr->typePtr != &tclStringType)) {
+	 	if ((objPtr->typePtr) && (objPtr->typePtr != &tclStringType)) {
 		    /* Prevent shimmer of non-string types. */
 		    allowUniChar = 0;
 		}
 	    }
 	} else {

Index: tests/append.test
==================================================================
--- tests/append.test
+++ tests/append.test
@@ -70,19 +70,19 @@
     set x \uD83D$x
 } -result \uD83D\uDE02
 test append-3.7 {append \xC0 \x80} -constraints testbytestring -body {
     set x [testbytestring \xC0]
     string length [append x [testbytestring \x80]]
-} -result 2
+} -result 1
 test append-3.8 {append \xC0 \x80} -constraints testbytestring -body {
     set x [testbytestring \xC0]
     string length $x[testbytestring \x80]
-} -result 2
+} -result 1
 test append-3.9 {append \xC0 \x80} -constraints testbytestring -body {
     set x [testbytestring \x80]
     string length [testbytestring \xC0]$x
-} -result 2
+} -result 1
 test append-3.10 {append surrogates} -body {
     set x \uD83D
     string range $x 0 end
     append x \uDE02
 } -result [string range \uD83D\uDE02 0 end]

Index: tests/utf.test
==================================================================
--- tests/utf.test
+++ tests/utf.test
@@ -93,15 +93,15 @@
     return $hi\uDE02
 } \uD83D\uDE02
 test utf-1.16 {Tcl_UniCharToUtf: \xC0 + \x80} testbytestring {
     set lo [testbytestring \x80]
     string length [testbytestring \xC0]$lo
-} 2
+} 1
 test utf-1.17 {Tcl_UniCharToUtf: \xC0 + \x80} testbytestring {
     set hi [testbytestring \xC0]
     string length $hi[testbytestring \x80]
-} 2
+} 1
 test utf-1.18 {Tcl_UniCharToUtf: surrogate pairs from concat} {
     string cat \uD83D \uDE02
 } \uD83D\uDE02
 
 test utf-2.1 {Tcl_UtfToUniChar: low ascii} {