diff --git a/regression/ansi-c/sizeof4/test.desc b/regression/ansi-c/sizeof4/test.desc
index fc2b1874059..466da18b2b5 100644
--- a/regression/ansi-c/sizeof4/test.desc
+++ b/regression/ansi-c/sizeof4/test.desc
@@ -1,4 +1,4 @@
-KNOWNBUG
+CORE
 main.c
 
 ^EXIT=0$
diff --git a/src/ansi-c/c_typecheck_expr.cpp b/src/ansi-c/c_typecheck_expr.cpp
index 406671379a9..975123572cd 100644
--- a/src/ansi-c/c_typecheck_expr.cpp
+++ b/src/ansi-c/c_typecheck_expr.cpp
@@ -950,7 +950,14 @@ void c_typecheck_baset::typecheck_expr_sizeof(exprt &expr)
   }
   else
   {
-    type.swap(to_unary_expr(expr).op().type());
+    const exprt &op = to_unary_expr(as_const(expr)).op();
+    // This is one of the few places where it's detectable
+    // that we are using "bool" for boolean operators instead
+    // of "int". We convert for this reason.
+    if(op.type().id() == ID_bool)
+      type = signed_int_type();
+    else
+      type = op.type();
   }
 
   exprt new_expr;