diff --git a/tgt-vhdl/cast.cc b/tgt-vhdl/cast.cc
index 1612e6514..e1568929f 100644
--- a/tgt-vhdl/cast.cc
+++ b/tgt-vhdl/cast.cc
@@ -28,10 +28,12 @@
 
 vhdl_expr *vhdl_expr::cast(const vhdl_type *to)
 {
-   //std::cout << "Cast: from=" << type_->get_string()
-   //          << " (" << type_->get_width() << ") "
-   //          << " to=" << to->get_string() << " ("
-   //          << to->get_width() << ")" << std::endl;
+#if 0
+   std::cout << "Cast: from=" << type_->get_string()
+             << " (" << type_->get_width() << ") "
+             << " to=" << to->get_string() << " ("
+             << to->get_width() << ")" << std::endl;
+#endif
 
    // If this expression hasn't been given a type then
    // we can't generate any type conversion code
@@ -58,6 +60,8 @@ vhdl_expr *vhdl_expr::cast(const vhdl_type *to)
          return to_std_logic();
       case VHDL_TYPE_STRING:
          return to_string();
+      case VHDL_TYPE_STD_ULOGIC:
+         return to_std_ulogic();
       default:
          assert(false);
       }
@@ -206,6 +210,17 @@ vhdl_expr *vhdl_expr::to_std_logic()
    return NULL;
 }
 
+vhdl_expr *vhdl_expr::to_std_ulogic()
+{
+   if (type_->get_name() == VHDL_TYPE_STD_LOGIC) {
+      vhdl_fcall *f = new vhdl_fcall("std_logic", vhdl_type::std_logic());
+      f->add_expr(this);
+      return f;
+   }
+   else 
+      assert(false);
+}
+
 /*
  * Change the width of a signed/unsigned type.
  */
@@ -325,6 +340,11 @@ vhdl_expr *vhdl_const_bit::to_boolean()
    return new vhdl_const_bool(bit_ == '1');
 }
 
+vhdl_expr *vhdl_const_bit::to_std_ulogic()
+{
+   return this;
+}
+
 vhdl_expr *vhdl_const_bit::to_vector(vhdl_type_name_t name, int w)
 {
    // Zero-extend this bit to the correct width
diff --git a/tgt-vhdl/scope.cc b/tgt-vhdl/scope.cc
index bb932e374..c7caa9716 100644
--- a/tgt-vhdl/scope.cc
+++ b/tgt-vhdl/scope.cc
@@ -277,6 +277,7 @@ void draw_nexus(ivl_nexus_t nexus)
       
       switch (signal_type_of_nexus(nexus, width)) {
       case IVL_SIT_TRI:
+      case IVL_SIT_UWIRE:
          def = 'Z';
          break;
       case IVL_SIT_TRI0:
@@ -556,9 +557,13 @@ static void declare_one_signal(vhdl_entity *ent, ivl_signal_t sig,
       
       sig_type = new vhdl_type(*array_type);
    }
-   else
-      sig_type =
-         vhdl_type::type_for(ivl_signal_width(sig), ivl_signal_signed(sig) != 0);
+   else {
+      sig_type = vhdl_type::type_for(ivl_signal_width(sig),
+                                     ivl_signal_signed(sig) != 0,
+                                     0, ivl_signal_type(sig) == IVL_SIT_UWIRE);
+
+      
+   }
    
    ivl_signal_port_t mode = ivl_signal_port(sig);
    switch (mode) {
diff --git a/tgt-vhdl/vhdl_syntax.hh b/tgt-vhdl/vhdl_syntax.hh
index 5d8ab2f83..80076f1c1 100644
--- a/tgt-vhdl/vhdl_syntax.hh
+++ b/tgt-vhdl/vhdl_syntax.hh
@@ -50,6 +50,7 @@ public:
    virtual vhdl_expr *to_boolean();
    virtual vhdl_expr *to_integer();
    virtual vhdl_expr *to_std_logic();
+   virtual vhdl_expr *to_std_ulogic();
    virtual vhdl_expr *to_vector(vhdl_type_name_t name, int w);
    virtual vhdl_expr *to_string();
    virtual void find_vars(vhdl_var_set_t& read) {}
@@ -211,6 +212,7 @@ public:
    vhdl_expr *to_boolean();
    vhdl_expr *to_integer();
    vhdl_expr *to_vector(vhdl_type_name_t name, int w);
+   vhdl_expr *to_std_ulogic();
 private:
    char bit_;
 };
diff --git a/tgt-vhdl/vhdl_type.cc b/tgt-vhdl/vhdl_type.cc
index 9442826c3..c448f6a5e 100644
--- a/tgt-vhdl/vhdl_type.cc
+++ b/tgt-vhdl/vhdl_type.cc
@@ -24,12 +24,16 @@
 #include <sstream>
 #include <iostream>
 
-
 vhdl_type *vhdl_type::std_logic()
 {
    return new vhdl_type(VHDL_TYPE_STD_LOGIC);
 }
 
+vhdl_type *vhdl_type::std_ulogic()
+{
+   return new vhdl_type(VHDL_TYPE_STD_ULOGIC);
+}
+
 vhdl_type *vhdl_type::string()
 {
    return new vhdl_type(VHDL_TYPE_STRING);
@@ -79,6 +83,8 @@ std::string vhdl_type::get_string() const
    switch (name_) {
    case VHDL_TYPE_STD_LOGIC:
       return std::string("std_logic");
+   case VHDL_TYPE_STD_ULOGIC:
+      return std::string("std_ulogic");
    case VHDL_TYPE_STD_LOGIC_VECTOR:
       return std::string("std_logic_vector");      
    case VHDL_TYPE_STRING:
@@ -167,10 +173,15 @@ vhdl_type *vhdl_type::std_logic_vector(int msb, int lsb)
    return new vhdl_type(VHDL_TYPE_STD_LOGIC_VECTOR, msb, lsb);
 }
 
-vhdl_type *vhdl_type::type_for(int width, bool issigned, int lsb)
+vhdl_type *vhdl_type::type_for(int width, bool issigned,
+                               int lsb, bool unresolved)
 {
-   if (width == 1)
-      return vhdl_type::std_logic();
+   if (width == 1) {
+      if (unresolved)
+         return vhdl_type::std_ulogic();
+      else
+         return vhdl_type::std_logic();
+   }
    else if (issigned)
       return vhdl_type::nsigned(width, lsb);
    else
diff --git a/tgt-vhdl/vhdl_type.hh b/tgt-vhdl/vhdl_type.hh
index 3d551a3f2..9786ab9ad 100644
--- a/tgt-vhdl/vhdl_type.hh
+++ b/tgt-vhdl/vhdl_type.hh
@@ -25,6 +25,7 @@
 
 enum vhdl_type_name_t {
    VHDL_TYPE_STD_LOGIC,
+   VHDL_TYPE_STD_ULOGIC,
    VHDL_TYPE_STD_LOGIC_VECTOR,
    VHDL_TYPE_STRING,
    VHDL_TYPE_LINE,
@@ -71,6 +72,7 @@ public:
    
    // Common types
    static vhdl_type *std_logic();
+   static vhdl_type *std_ulogic();
    static vhdl_type *string();
    static vhdl_type *line();
    static vhdl_type *std_logic_vector(int msb, int lsb);
@@ -80,7 +82,8 @@ public:
    static vhdl_type *boolean();
    static vhdl_type *time();
 
-   static vhdl_type *type_for(int width, bool issigned, int lsb=0);
+   static vhdl_type *type_for(int width, bool issigned,
+                              int lsb=0, bool unresolved=false);
    static vhdl_type *array_of(vhdl_type *b, std::string &n, int m, int l);
 protected:
    vhdl_type_name_t name_;