--- a/SignedByteArray.st	Sun Jun 09 15:26:37 2019 +0200
+++ b/SignedByteArray.st	Sun Jun 09 15:31:25 2019 +0200
@@ -119,35 +119,42 @@
     REGISTER OBJ slf;
     REGISTER OBJ cls;
 
-    if (__bothSmallInteger(index, value)) {
-        val = __intVal(value);
-        if ((val >= -128) && (val <= 127)) {
-            indx = __intVal(index) - 1;
-            slf = self;
-            if ((cls = __qClass(slf)) != @global(SignedByteArray)) {
-                if (((INT)__ClassInstPtr(cls)->c_flags & __MASKSMALLINT(ARRAYMASK))
-                    != __MASKSMALLINT(BYTEARRAY)) {
-                    goto fail;
+    if (! __isImmutable(self)) {
+        if (__bothSmallInteger(index, value)) {
+            val = __intVal(value);
+            if ((val >= -128) && (val <= 127)) {
+                indx = __intVal(index) - 1;
+                slf = self;
+                if ((cls = __qClass(slf)) != @global(SignedByteArray)) {
+                    if (((INT)__ClassInstPtr(cls)->c_flags & __MASKSMALLINT(ARRAYMASK))
+                        != __MASKSMALLINT(BYTEARRAY)) {
+                        goto fail;
+                    }
+                    if (indx < 0) goto fail;
+                    indx += __OBJS2BYTES__(__intVal(__ClassInstPtr(cls)->c_ninstvars));
                 }
-                if (indx < 0) goto fail;
-                indx += __OBJS2BYTES__(__intVal(__ClassInstPtr(cls)->c_ninstvars));
-            }
-            nIndex = __byteArraySize(slf);
-            if ((unsigned)indx < (unsigned)nIndex) {
-                __ByteArrayInstPtr(slf)->ba_element[indx] = val;
-                RETURN ( value );
+                nIndex = __byteArraySize(slf);
+                if ((unsigned)indx < (unsigned)nIndex) {
+                    __ByteArrayInstPtr(slf)->ba_element[indx] = val;
+                    RETURN ( value );
+                }
             }
         }
     }
   fail: ;
 %}.
+    "/ arrive here only in case of an error
+    self isImmutable ifTrue:[
+        self noModificationError
+    ].    
     ^ super basicAt:index put:value
 
     "
        (self new:5) basicAt:1 put:-1; yourself
     "
 
-    "Modified: 19.4.1996 / 11:14:40 / cg"
+    "Modified: / 19-04-1996 / 11:14:40 / cg"
+    "Modified: / 09-06-2019 / 15:29:50 / Claus Gittinger"
 ! !
 
 !SignedByteArray methodsFor:'converting'!
@@ -327,6 +334,10 @@
         }
     }
 %}.
+    "/ arrive here only in case of an error
+    self isImmutable ifTrue:[
+        self noModificationError
+    ].    
     "
      fall back in case of non-integer index or out-of-bound index/value;
      will eventually lead to an out-of-bound signal raise
@@ -338,6 +349,8 @@
      (self new:20) from:10 to:20 put:-5
      (self new:20) from:1 to:10 put:-5
     "
+
+    "Modified: / 09-06-2019 / 15:30:52 / Claus Gittinger"
 ! !
 
 !SignedByteArray methodsFor:'queries'!