diff --git a/src/stringobj.c b/src/stringobj.c
index c59e3e1879..613ec399ae 100644
--- a/src/stringobj.c
+++ b/src/stringobj.c
@@ -198,17 +198,17 @@ void LoadChar( Obj c )
 
 /****************************************************************************
 **
-*F  FuncEmptyString( <self>, <len> ) . . . . . . . empty string with space
-*
-* Returns an empty string, but with space for len characters preallocated.
-*
+*F  FuncEmptyString( <self>, <len> ) . . . . . . . .  empty string with space
+**
+**  Returns an empty string, but with space for len characters preallocated.
+**
 */
 Obj    FuncEmptyString( Obj self, Obj len )
 {
     Obj                 new;
-    while ( ! IS_INTOBJ(len) ) {
+    while ( ! IS_NONNEG_INTOBJ(len) ) {
         len = ErrorReturnObj(
-            "<len> must be an integer (not a %s)",
+            "<len> must be an non-negative integer (not a %s)",
             (Int)TNAM_OBJ(len), 0L,
             "you can replace <len> via 'return <len>;'" );
     }
@@ -220,11 +220,11 @@ Obj    FuncEmptyString( Obj self, Obj len )
 
 /****************************************************************************
 **
-*F  FuncShrinkAllocationString( <self>, <str> )  . . give back unneeded memory
-*
-*  Shrinks the bag of <str> to minimal possible size (possibly converts to 
-*  compact representation).
-*
+*F  FuncShrinkAllocationString( <self>, <str> ) . . give back unneeded memory
+**
+**  Shrinks the bag of <str> to minimal possible size (possibly converts to
+**  compact representation).
+**
 */
 Obj   FuncShrinkAllocationString( Obj self, Obj str )
 {
@@ -406,19 +406,22 @@ Obj FuncSTRING_SINTLIST (
    * integers ? */
 
   /* general code */
-  if (! IS_RANGE(val) ) {
-    if (! IS_PLIST(val)) {
+  while (!IS_RANGE(val) && !IS_PLIST(val)) {
+again:
        val = ErrorReturnObj(
-           "<val> must be a plain list or range, not a %s)",
+           "<val> must be a plain list of small integers or a range, not a %s",
            (Int)TNAM_OBJ(val), 0L,
            "you can replace <val> via 'return <val>;'" );
-    }
-       
+  }
+  if (! IS_RANGE(val) ) {
     l=LEN_PLIST(val);
     n=NEW_STRING(l);
     p=CHARS_STRING(n);
     for (i=1;i<=l;i++) {
-      *p++=CHAR_SINT(INT_INTOBJ(ELM_PLIST(val,i)));
+      Obj x = ELM_PLIST(val,i);
+      if (!IS_INTOBJ(x))
+        goto again;
+      *p++=CHAR_SINT(INT_INTOBJ(x));
     }
   }
   else {
@@ -434,7 +437,6 @@ Obj FuncSTRING_SINTLIST (
 
   }
 
-  CHANGED_BAG(n);
   return n;
 }
 
@@ -464,12 +466,10 @@ Obj FuncREVNEG_STRING (
   q=CHARS_STRING(n);
   j=l-1;
   for (i=1;i<=l;i++) {
-    /* *q++=CHAR_SINT(-SINT_CHAR(p[j])); */
     *q++=-p[j];
     j--;
   }
 
-  CHANGED_BAG(n);
   return n;
 }
 
@@ -1084,8 +1084,6 @@ void AssString (
 
     /* now perform the assignment and return the assigned value            */
     SET_ELM_STRING( list, pos, val ); 
-    /*    CHARS_STRING(list)[pos-1] = CHAR_VALUE(val); */
-    CHANGED_BAG( list );
   }
 }    
 
@@ -1377,7 +1375,6 @@ void ConvString (
     ResizeBag( string, SIZEBAG_STRINGLEN(lenString) );
     /* copy data area from tmp */
     memcpy(ADDR_OBJ(string), CONST_ADDR_OBJ(tmp), SIZE_OBJ(tmp));
-    CHANGED_BAG(string);
 }
 
 
@@ -1431,17 +1428,6 @@ Obj MakeString2(const Char *cstr1, const Char *cstr2)
   return result;
 }
 
-Obj MakeString3(const Char *cstr1, const Char *cstr2, const Char *cstr3)
-{
-  Obj result;
-  size_t len1 = strlen(cstr1), len2 = strlen(cstr2), len3 = strlen(cstr3);
-  result = NEW_STRING(len1 + len2 + len3);
-  memcpy(CSTR_STRING(result), cstr1, len1);
-  memcpy(CSTR_STRING(result)+len1, cstr2, len2);
-  memcpy(CSTR_STRING(result)+len1+len2, cstr3, len3);
-  return result;
-}
-
 Obj MakeImmString2(const Char *cstr1, const Char *cstr2)
 {
   Obj result = MakeString2(cstr1, cstr2);
@@ -1449,13 +1435,6 @@ Obj MakeImmString2(const Char *cstr1, const Char *cstr2)
   return result;
 }
 
-Obj MakeImmString3(const Char *cstr1, const Char *cstr2, const Char *cstr3)
-{
-  Obj result = MakeString3(cstr1, cstr2, cstr3);
-  MakeImmutableString(result);
-  return result;
-}
-
 Obj ConvImmString(Obj str)
 {
   Obj result;
@@ -1511,12 +1490,11 @@ Obj FuncCONV_STRING (
     Obj                 string )
 {
     /* check whether <string> is a string                                  */
-    if ( ! IS_STRING( string ) ) {
+    while ( ! IS_STRING( string ) ) {
         string = ErrorReturnObj(
             "ConvString: <string> must be a string (not a %s)",
             (Int)TNAM_OBJ(string), 0L,
             "you can replace <string> via 'return <string>;'" );
-        return FuncCONV_STRING( self, string );
     }
 
     /* convert to the string representation                                */
@@ -1549,12 +1527,11 @@ Obj FuncCOPY_TO_STRING_REP (
     Obj                 obj )
 {
     /* check whether <obj> is a string                                  */
-    if (!IS_STRING(obj)) {
+    while (!IS_STRING(obj)) {
         obj = ErrorReturnObj(
-            "ConvString: <string> must be a string (not a %s)",
+            "CopyToStringRep: <string> must be a string (not a %s)",
             (Int)TNAM_OBJ(obj), 0L,
             "you can replace <string> via 'return <string>;'" );
-        return FuncCOPY_TO_STRING_REP( self, obj );
     }
     return CopyToStringRep(obj);
 }
@@ -1645,12 +1622,11 @@ Obj FuncNormalizeWhitespace (
   Int i, j, len, white;
 
   /* check whether <string> is a string                                  */
-  if ( ! IsStringConv( string ) ) {
+  while ( ! IsStringConv( string ) ) {
     string = ErrorReturnObj(
 	     "NormalizeWhitespace: <string> must be a string (not a %s)",
 	     (Int)TNAM_OBJ(string), 0L,
 	     "you can replace <string> via 'return <string>;'" );
-    return FuncNormalizeWhitespace( self, string );
   }
   
   len = GET_LEN_STRING(string);
@@ -1701,21 +1677,19 @@ Obj FuncREMOVE_CHARACTERS (
   UInt1 REMCHARLIST[256] = {0};
 
   /* check whether <string> is a string                                  */
-  if ( ! IsStringConv( string ) ) {
+  while ( ! IsStringConv( string ) ) {
     string = ErrorReturnObj(
 	     "RemoveCharacters: first argument <string> must be a string (not a %s)",
 	     (Int)TNAM_OBJ(string), 0L,
 	     "you can replace <string> via 'return <string>;'" );
-    return FuncREMOVE_CHARACTERS( self, string, rem );
   }
   
   /* check whether <rem> is a string                                  */
-  if ( ! IsStringConv( rem ) ) {
+  while ( ! IsStringConv( rem ) ) {
     rem = ErrorReturnObj(
 	     "RemoveCharacters: second argument <rem> must be a string (not a %s)",
 	     (Int)TNAM_OBJ(rem), 0L,
 	     "you can replace <rem> via 'return <rem>;'" );
-    return FuncREMOVE_CHARACTERS( self, string, rem );
   }
   
   /* set REMCHARLIST by setting positions of characters in rem to 1 */
@@ -1757,32 +1731,28 @@ Obj FuncTranslateString (
   Int j, len;
 
   /* check whether <string> is a string                                  */
-  if ( ! IsStringConv( string ) ) {
+  while ( ! IsStringConv( string ) ) {
     string = ErrorReturnObj(
-	     "RemoveCharacters: first argument <string> must be a string (not a %s)",
+	     "TranslateString: first argument <string> must be a string (not a %s)",
 	     (Int)TNAM_OBJ(string), 0L,
 	     "you can replace <string> via 'return <string>;'" );
-    return FuncTranslateString( self, string, trans );
   }
   
-  /* check whether <trans> is a string                                  */
-  if ( ! IsStringConv( trans ) ) {
-    trans = ErrorReturnObj(
-	     "RemoveCharacters: second argument <trans> must be a string (not a %s)",
-	     (Int)TNAM_OBJ(trans), 0L,
-	     "you can replace <trans> via 'return <trans>;'" );
-    return FuncTranslateString( self, string, trans );
-  }
- 
-  /* check if string has length at least 256 */
-  if ( GET_LEN_STRING( trans ) < 256 ) {
-    trans = ErrorReturnObj(
-	     "RemoveCharacters: second argument <trans> must have length >= 256",
-	     0L, 0L,
-	     "you can replace <trans> via 'return <trans>;'" );
-    return FuncTranslateString( self, string, trans );
+  // check whether <trans> is a string of length at least 256
+  while ( ! IsStringConv( trans ) || GET_LEN_STRING( trans ) < 256 ) {
+    if ( ! IsStringConv( trans ) ) {
+      trans = ErrorReturnObj(
+           "TranslateString: second argument <trans> must be a string (not a %s)",
+           (Int)TNAM_OBJ(trans), 0L,
+           "you can replace <trans> via 'return <trans>;'" );
+    } else if ( GET_LEN_STRING( trans ) < 256 ) {
+      trans = ErrorReturnObj(
+           "TranslateString: second argument <trans> must have length >= 256",
+           0L, 0L,
+           "you can replace <trans> via 'return <trans>;'" );
+    }
   }
-  
+
   /* now change string in place */
   len = GET_LEN_STRING(string);
   s = CHARS_STRING(string);
@@ -1816,30 +1786,27 @@ Obj FuncSplitStringInternal (
   UInt1 SPLITSTRINGWSPACE[256] = { 0 };
 
   /* check whether <string> is a string                                  */
-  if ( ! IsStringConv( string ) ) {
+  while ( ! IsStringConv( string ) ) {
     string = ErrorReturnObj(
 	     "SplitString: first argument <string> must be a string (not a %s)",
 	     (Int)TNAM_OBJ(string), 0L,
 	     "you can replace <string> via 'return <string>;'" );
-    return FuncSplitStringInternal( self, string, seps, wspace );
   }
   
   /* check whether <seps> is a string                                  */
-  if ( ! IsStringConv( seps ) ) {
+  while ( ! IsStringConv( seps ) ) {
     seps = ErrorReturnObj(
 	     "SplitString: second argument <seps> must be a string (not a %s)",
 	     (Int)TNAM_OBJ(seps), 0L,
 	     "you can replace <seps> via 'return <seps>;'" );
-    return FuncSplitStringInternal( self, string, seps, wspace );
   }
   
   /* check whether <wspace> is a string                                  */
-  if ( ! IsStringConv( wspace ) ) {
+  while ( ! IsStringConv( wspace ) ) {
     wspace = ErrorReturnObj(
 	     "SplitString: third argument <wspace> must be a string (not a %s)",
 	     (Int)TNAM_OBJ(wspace), 0L,
 	     "you can replace <wspace> via 'return <wspace>;'" );
-    return FuncSplitStringInternal( self, string, seps, wspace );
   }
   
   /* set SPLITSTRINGSEPS by setting positions of characters in rem to 1 */
diff --git a/src/stringobj.h b/src/stringobj.h
index b511226fc4..4a04ee8462 100644
--- a/src/stringobj.h
+++ b/src/stringobj.h
@@ -367,10 +367,8 @@ static inline Obj MakeImmString(const Char * cstr)
 
 
 Obj MakeString2(const Char *cstr1, const Char *cstr2);
-Obj MakeString3(const Char *cstr1, const Char *cstr2, const Char *cstr3);
 
 Obj MakeImmString2(const Char *cstr1, const Char *cstr2);
-Obj MakeImmString3(const Char *cstr1, const Char *cstr2, const Char *cstr3);
 Obj ConvImmString(Obj str);
 
 
diff --git a/tst/testinstall/kernel/streams.tst b/tst/testinstall/kernel/streams.tst
index 5d634e398e..baa322d8e8 100644
--- a/tst/testinstall/kernel/streams.tst
+++ b/tst/testinstall/kernel/streams.tst
@@ -66,6 +66,12 @@ gap> INPUT_TEXT_FILE(fail);
 Error, <filename> must be a string (not a boolean or fail)
 gap> IS_END_OF_FILE(fail);
 Error, <fid> must be an integer (not a boolean or fail)
+gap> IS_END_OF_FILE(-1);
+fail
+gap> IS_END_OF_FILE(0);
+false
+gap> IS_END_OF_FILE(254);
+fail
 gap> OUTPUT_TEXT_FILE(fail, fail);
 Error, <filename> must be a string (not a boolean or fail)
 gap> OUTPUT_TEXT_FILE("test", fail);
@@ -74,8 +80,20 @@ Error, <append> must be a boolean (not a boolean or fail)
 #
 gap> POSITION_FILE(fail);
 Error, <fid> must be an integer (not a boolean or fail)
+gap> POSITION_FILE(-1);
+fail
+gap> IsInt(POSITION_FILE(4));
+true
+gap> POSITION_FILE(254);
+fail
+
+#
 gap> READ_BYTE_FILE(fail);
 Error, <fid> must be an integer (not a boolean or fail)
+gap> READ_BYTE_FILE(-1);
+fail
+
+#
 gap> READ_LINE_FILE(fail);
 Error, <fid> must be an integer (not a boolean or fail)
 gap> READ_ALL_FILE(fail,fail);
@@ -86,10 +104,20 @@ gap> SEEK_POSITION_FILE(fail,fail);
 Error, <fid> must be an integer (not a boolean or fail)
 gap> SEEK_POSITION_FILE(1,fail);
 Error, <pos> must be an integer (not a boolean or fail)
+
+#
 gap> WRITE_BYTE_FILE(fail,fail);
 Error, <fid> must be an integer (not a boolean or fail)
 gap> WRITE_BYTE_FILE(1,fail);
 Error, <ch> must be an integer (not a boolean or fail)
+gap> WRITE_BYTE_FILE(-1,65);
+fail
+gap> WRITE_BYTE_FILE(0,65);
+true
+gap> WRITE_BYTE_FILE(254,65);
+fail
+
+#
 gap> READ_STRING_FILE(fail);
 Error, <fid> must be an integer (not a boolean or fail)
 
diff --git a/tst/testinstall/kernel/stringobj.tst b/tst/testinstall/kernel/stringobj.tst
new file mode 100644
index 0000000000..b27bf85803
--- /dev/null
+++ b/tst/testinstall/kernel/stringobj.tst
@@ -0,0 +1,126 @@
+#
+# Tests for functions defined in src/strinobj.c
+#
+gap> START_TEST("kernel/strinobj.tst");
+
+#
+gap> s := EmptyString(2);
+""
+gap> EmptyString(-1);
+Error, <len> must be an non-negative integer (not a integer)
+
+#
+gap> ShrinkAllocationString(s);
+gap> ShrinkAllocationString(1);
+Error, <str> must be a string, not a integer)
+
+#
+gap> CHAR_INT(fail);
+Error, <val> must be an integer (not a boolean or fail)
+gap> CHAR_INT(-1);
+Error, <val> must be an integer between 0 and 255
+gap> CHAR_INT(65);
+'A'
+
+#
+gap> INT_CHAR(1);
+Error, <val> must be a character (not a integer)
+gap> INT_CHAR('A');
+65
+
+#
+gap> CHAR_SINT(fail);
+Error, <val> must be an integer (not a boolean or fail)
+gap> CHAR_SINT(255);
+Error, <val> must be an integer between -128 and 127
+gap> CHAR_SINT(65);
+'A'
+
+#
+gap> SINT_CHAR(1);
+Error, <val> must be a character (not a integer)
+gap> SINT_CHAR('A');
+65
+
+#
+gap> INTLIST_STRING("ABC", 1);
+[ 65, 66, 67 ]
+gap> INTLIST_STRING("ABC", -1);
+[ 65, 66, 67 ]
+gap> INTLIST_STRING(1, -1);
+Error, <val> must be a string, not a integer)
+
+#
+gap> SINTLIST_STRING("ABC");
+[ 65, 66, 67 ]
+gap> SINTLIST_STRING(1);
+Error, <val> must be a string, not a integer)
+
+#
+gap> STRING_SINTLIST([ 65, 66, 67 ]);
+"ABC"
+gap> STRING_SINTLIST([ 65 .. 67 ]);
+"ABC"
+gap> STRING_SINTLIST(1);
+Error, <val> must be a plain list of small integers or a range, not a integer
+gap> STRING_SINTLIST([ 'B' ]);
+Error, <val> must be a plain list of small integers or a range, not a list (pl\
+ain,hom)
+
+#
+gap> REVNEG_STRING(1);
+Error, <val> must be a string, not a integer)
+
+#
+gap> CONV_STRING(1);
+Error, ConvString: <string> must be a string (not a integer)
+
+#
+gap> COPY_TO_STRING_REP(1);
+Error, CopyToStringRep: <string> must be a string (not a integer)
+
+#
+gap> POSITION_SUBSTRING("abc","x",0);
+fail
+gap> POSITION_SUBSTRING("abc","b",0);
+2
+gap> POSITION_SUBSTRING("abc","b",3);
+fail
+gap> POSITION_SUBSTRING(1,2,3);
+Error, POSITION_SUBSTRING: <string> must be a string (not a integer)
+gap> POSITION_SUBSTRING("abc",2,3);
+Error, POSITION_SUBSTRING: <substr> must be a string (not a integer)
+gap> POSITION_SUBSTRING("abc","b",-1);
+Error, POSITION_SUBSTRING: <off> must be a non-negative integer (not a integer\
+)
+
+#
+gap> s:="  abc\n  xyz\n";; NormalizeWhitespace(s); s;
+"abc xyz"
+gap> NormalizeWhitespace(1);
+Error, NormalizeWhitespace: <string> must be a string (not a integer)
+
+#
+gap> s:="abcdabcd";; REMOVE_CHARACTERS(s, "db"); s;
+"acac"
+gap> REMOVE_CHARACTERS(1,1);
+Error, RemoveCharacters: first argument <string> must be a string (not a integ\
+er)
+gap> REMOVE_CHARACTERS(s,1);
+Error, RemoveCharacters: second argument <rem> must be a string (not a integer\
+)
+
+#
+gap> s:="abc";; TranslateString(s,UPPERCASETRANSTABLE); s;
+"ABC"
+gap> TranslateString(1,1);
+Error, TranslateString: first argument <string> must be a string (not a intege\
+r)
+gap> TranslateString("abc",1);
+Error, TranslateString: second argument <trans> must be a string (not a intege\
+r)
+gap> TranslateString("abc","def");
+Error, TranslateString: second argument <trans> must have length >= 256
+
+#
+gap> STOP_TEST("kernel/strinobj.tst", 1);