diff --git a/source/compiler/sc1.c b/source/compiler/sc1.c
index 590b7e6..f69f439 100644
--- a/source/compiler/sc1.c
+++ b/source/compiler/sc1.c
@@ -1098,7 +1098,11 @@ static void parseoptions(int argc,char **argv,char *oname,char *ename,char *pnam
         skipinput=atoi(option_value(ptr));
         break;
       case 't':
-        sc_tabsize=atoi(option_value(ptr));
+        i=atoi(option_value(ptr));
+        if (i>0)
+          sc_tabsize=i;
+        else
+          about();
         break;
       case 'v':
         verbosity= isdigit(*option_value(ptr)) ? atoi(option_value(ptr)) : 2;
diff --git a/source/compiler/sc2.c b/source/compiler/sc2.c
index 14d62de..6315ca3 100644
--- a/source/compiler/sc2.c
+++ b/source/compiler/sc2.c
@@ -1144,7 +1144,8 @@ static int command(void)
         } else if (strcmp(str,"tabsize")==0) {
           cell val;
           preproc_expr(&val,NULL);
-          sc_tabsize=(int)val;
+          if (val>0)
+            sc_tabsize=(int)val;
         } else if (strcmp(str,"align")==0) {
           sc_alignnext=TRUE;
         } else if (strcmp(str,"unused")==0) {