Index: gcc/fortran/match.c
===================================================================
--- gcc/fortran/match.c	(revision 276271)
+++ gcc/fortran/match.c	(working copy)
@@ -4984,6 +4984,16 @@ gfc_match_call (void)
 	goto syntax;
     }
 
+  /* Walk the argument list looking for invalid BOZ.  */
+  for (a = arglist; a; a = a->next)
+    if (a->expr && a->expr->ts.type == BT_BOZ)
+      {
+	gfc_error ("A BOZ literal constant at %L cannot appear as an actual "
+		   "argument in a subroutine reference", &a->expr->where);
+	goto cleanup;
+      }
+
+
   /* If any alternate return labels were found, construct a SELECT
      statement that will jump to the right place.  */
 
Index: gcc/fortran/resolve.c
===================================================================
--- gcc/fortran/resolve.c	(revision 276271)
+++ gcc/fortran/resolve.c	(working copy)
@@ -3242,6 +3242,21 @@ resolve_function (gfc_expr *expr)
   if (expr->expr_type != EXPR_FUNCTION)
     return t;
 
+  /* Walk the argument list looking for invalid BOZ.  */
+  if (expr->value.function.esym)
+    {
+      gfc_actual_arglist *a;
+
+      for (a = expr->value.function.actual; a; a = a->next)
+	if (a->expr && a->expr->ts.type == BT_BOZ)
+	  {
+	    gfc_error ("A BOZ literal constant at %L cannot appear as an "
+			"actual argument in a function reference",
+			&a->expr->where);
+	    return false;
+	  }
+    }
+
   temp = need_full_assumed_size;
   need_full_assumed_size = 0;
 
Index: gcc/testsuite/gfortran.dg/pr91943.f90
===================================================================
--- gcc/testsuite/gfortran.dg/pr91943.f90	(nonexistent)
+++ gcc/testsuite/gfortran.dg/pr91943.f90	(working copy)
@@ -0,0 +1,7 @@
+! { dg-do compile }
+! PR fortran/91943
+! Code contributed by Gerhard Steinmetz
+program p
+   print *, f(b'1001')  ! { dg-error "cannot appear as an actual argument" }
+   call sub(b'1001')    ! { dg-error "cannot appear as an actual argument" }
+end