diff --git a/tgt-vhdl/vhdl_element.cc b/tgt-vhdl/vhdl_element.cc
index 5391736f7..cdbd1fcff 100644
--- a/tgt-vhdl/vhdl_element.cc
+++ b/tgt-vhdl/vhdl_element.cc
@@ -38,14 +38,14 @@ int indent(int level)
 /*
  * Emit a newline and indent to the correct level.
  */
-void newline(std::ofstream &of, int level)
+void newline(std::ostream &of, int level)
 {
    of << std::endl;
    while (level--)
       of << ' ';
 }
 
-void blank_line(std::ofstream &of, int level)
+void blank_line(std::ostream &of, int level)
 {
    of << std::endl;
    newline(of, level);
@@ -61,7 +61,7 @@ void vhdl_element::set_comment(std::string comment)
  * a line before the element (end_of_line is false) or at the
  * end of the line containing the element (end_of_line is true).
  */
-void vhdl_element::emit_comment(std::ofstream &of, int level,
+void vhdl_element::emit_comment(std::ostream &of, int level,
                                 bool end_of_line) const
 {
    if (comment_.size() > 0) {
diff --git a/tgt-vhdl/vhdl_element.hh b/tgt-vhdl/vhdl_element.hh
index f73ea0949..4bd6b3c05 100644
--- a/tgt-vhdl/vhdl_element.hh
+++ b/tgt-vhdl/vhdl_element.hh
@@ -34,11 +34,11 @@ class vhdl_element {
 public:
    virtual ~vhdl_element() {}
    
-   virtual void emit(std::ofstream &of, int level=0) const = 0;
+   virtual void emit(std::ostream &of, int level=0) const = 0;
 
    void set_comment(std::string comment);
 protected:
-   void emit_comment(std::ofstream &of, int level,
+   void emit_comment(std::ostream &of, int level,
                      bool end_of_line=false) const;
 private:
    std::string comment_;
@@ -47,8 +47,8 @@ private:
 typedef std::list<vhdl_element*> element_list_t;
 
 int indent(int level);
-void newline(std::ofstream &of, int level);
-void blank_line(std::ofstream &of, int level);
+void newline(std::ostream &of, int level);
+void blank_line(std::ostream &of, int level);
 
 #endif
 
diff --git a/tgt-vhdl/vhdl_helper.hh b/tgt-vhdl/vhdl_helper.hh
index c1f9499ab..a3f6f0704 100644
--- a/tgt-vhdl/vhdl_helper.hh
+++ b/tgt-vhdl/vhdl_helper.hh
@@ -26,7 +26,7 @@
 #include <cassert>
 
 template <class T>
-void emit_children(std::ofstream &of,
+void emit_children(std::ostream &of,
                    const std::list<T*> &children,
                    int level, const char *delim="") 
 {      
diff --git a/tgt-vhdl/vhdl_syntax.cc b/tgt-vhdl/vhdl_syntax.cc
index 87629a46f..2d4d1e984 100644
--- a/tgt-vhdl/vhdl_syntax.cc
+++ b/tgt-vhdl/vhdl_syntax.cc
@@ -80,7 +80,7 @@ void vhdl_entity::add_port(vhdl_port_decl *decl)
    ports_.add_decl(decl);
 }
 
-void vhdl_entity::emit(std::ofstream &of, int level) const
+void vhdl_entity::emit(std::ostream &of, int level) const
 {
    // Pretty much every design will use std_logic so we
    // might as well include it by default
@@ -122,7 +122,7 @@ void vhdl_arch::add_stmt(vhdl_conc_stmt *stmt)
    stmts_.push_back(stmt);
 }
 
-void vhdl_arch::emit(std::ofstream &of, int level) const
+void vhdl_arch::emit(std::ostream &of, int level) const
 {
    emit_comment(of, level);
    of << "architecture " << name_ << " of " << entity_;
@@ -139,7 +139,7 @@ void vhdl_process::add_sensitivity(const char *name)
    sens_.push_back(name);
 }
 
-void vhdl_process::emit(std::ofstream &of, int level) const
+void vhdl_process::emit(std::ostream &of, int level) const
 {
    // If there are no statements in the body, this process
    // can't possibly do anything, so don't bother to emit it
@@ -184,7 +184,7 @@ void stmt_container::add_stmt(vhdl_seq_stmt *stmt)
    stmts_.push_back(stmt);
 }
 
-void stmt_container::emit(std::ofstream &of, int level) const
+void stmt_container::emit(std::ostream &of, int level) const
 {
    emit_children<vhdl_seq_stmt>(of, stmts_, level);  
 }
@@ -210,7 +210,7 @@ void vhdl_comp_inst::map_port(const char *name, vhdl_expr *expr)
    mapping_.push_back(pmap);
 }
 
-void vhdl_comp_inst::emit(std::ofstream &of, int level) const
+void vhdl_comp_inst::emit(std::ostream &of, int level) const
 {
    emit_comment(of, level);
    of << inst_name_ << ": " << comp_name_;
@@ -258,7 +258,7 @@ vhdl_component_decl *vhdl_component_decl::component_decl_for(vhdl_entity *ent)
    return decl;
 }
 
-void vhdl_component_decl::emit(std::ofstream &of, int level) const
+void vhdl_component_decl::emit(std::ostream &of, int level) const
 {
    emit_comment(of, level);
    of << "component " << name_ << " is";
@@ -280,7 +280,7 @@ vhdl_wait_stmt::~vhdl_wait_stmt()
       delete expr_;
 }
 
-void vhdl_wait_stmt::emit(std::ofstream &of, int level) const
+void vhdl_wait_stmt::emit(std::ostream &of, int level) const
 {
    of << "wait";
 
@@ -318,7 +318,7 @@ void vhdl_decl::set_initial(vhdl_expr *initial)
    initial_ = initial;
 }
 
-void vhdl_port_decl::emit(std::ofstream &of, int level) const
+void vhdl_port_decl::emit(std::ostream &of, int level) const
 {
    of << name_ << " : ";
    
@@ -337,7 +337,7 @@ void vhdl_port_decl::emit(std::ofstream &of, int level) const
    type_->emit(of, level);
 }
 
-void vhdl_var_decl::emit(std::ofstream &of, int level) const
+void vhdl_var_decl::emit(std::ostream &of, int level) const
 {
    of << "variable " << name_ << " : ";
    type_->emit(of, level);
@@ -351,7 +351,7 @@ void vhdl_var_decl::emit(std::ofstream &of, int level) const
    emit_comment(of, level, true);
 }
 
-void vhdl_signal_decl::emit(std::ofstream &of, int level) const
+void vhdl_signal_decl::emit(std::ostream &of, int level) const
 {
    of << "signal " << name_ << " : ";
    type_->emit(of, level);
@@ -435,7 +435,7 @@ vhdl_expr_list::~vhdl_expr_list()
    delete_children<vhdl_expr>(exprs_);
 }
 
-void vhdl_expr_list::emit(std::ofstream &of, int level) const
+void vhdl_expr_list::emit(std::ostream &of, int level) const
 {
    of << "(";
    
@@ -450,7 +450,7 @@ void vhdl_expr_list::emit(std::ofstream &of, int level) const
    of << ")";
 }
 
-void vhdl_pcall_stmt::emit(std::ofstream &of, int level) const
+void vhdl_pcall_stmt::emit(std::ostream &of, int level) const
 {
    of << name_;
    if (!exprs_.empty())
@@ -464,7 +464,7 @@ vhdl_var_ref::~vhdl_var_ref()
       delete slice_;
 }
 
-void vhdl_var_ref::emit(std::ofstream &of, int level) const
+void vhdl_var_ref::emit(std::ostream &of, int level) const
 {
    of << name_;
    if (slice_) {
@@ -474,7 +474,7 @@ void vhdl_var_ref::emit(std::ofstream &of, int level) const
    }
 }
 
-void vhdl_const_string::emit(std::ofstream &of, int level) const
+void vhdl_const_string::emit(std::ostream &of, int level) const
 {
    // In some instances a string literal can be ambiguous between
    // a String type and some other types (e.g. std_logic_vector)
@@ -483,12 +483,12 @@ void vhdl_const_string::emit(std::ofstream &of, int level) const
    of << "String'(\"" << value_ << "\")";
 }
 
-void vhdl_null_stmt::emit(std::ofstream &of, int level) const
+void vhdl_null_stmt::emit(std::ostream &of, int level) const
 {
    of << "null;";
 }
 
-void vhdl_fcall::emit(std::ofstream &of, int level) const
+void vhdl_fcall::emit(std::ostream &of, int level) const
 {
    of << name_;
    exprs_.emit(of, level);
@@ -502,7 +502,7 @@ vhdl_abstract_assign_stmt::~vhdl_abstract_assign_stmt()
       delete after_;
 }
 
-void vhdl_nbassign_stmt::emit(std::ofstream &of, int level) const
+void vhdl_nbassign_stmt::emit(std::ostream &of, int level) const
 {
    lhs_->emit(of, level);
    of << " <= ";
@@ -516,7 +516,7 @@ void vhdl_nbassign_stmt::emit(std::ofstream &of, int level) const
    of << ";";
 }
 
-void vhdl_assign_stmt::emit(std::ofstream &of, int level) const
+void vhdl_assign_stmt::emit(std::ostream &of, int level) const
 {
    lhs_->emit(of, level);
    of << " := ";
@@ -569,7 +569,7 @@ vhdl_expr *vhdl_const_bits::cast(const vhdl_type *to)
       return vhdl_expr::cast(to);
 }
 
-void vhdl_const_bits::emit(std::ofstream &of, int level) const
+void vhdl_const_bits::emit(std::ostream &of, int level) const
 {
    if (qualified_)
       of << (signed_ ? "signed" : "unsigned") << "'(\"";
@@ -584,17 +584,17 @@ void vhdl_const_bits::emit(std::ofstream &of, int level) const
    of << (qualified_ ? "\")" : "\"");
 }
 
-void vhdl_const_bit::emit(std::ofstream &of, int level) const
+void vhdl_const_bit::emit(std::ostream &of, int level) const
 {
    of << "'" << vl_to_vhdl_bit(bit_) << "'";
 }
 
-void vhdl_const_int::emit(std::ofstream &of, int level) const
+void vhdl_const_int::emit(std::ostream &of, int level) const
 {
    of << value_;
 }
 
-void vhdl_const_time::emit(std::ofstream &of, int level) const
+void vhdl_const_time::emit(std::ostream &of, int level) const
 {
    of << value_;
    switch (units_) {
@@ -609,7 +609,7 @@ vhdl_cassign_stmt::~vhdl_cassign_stmt()
    delete rhs_;
 }
 
-void vhdl_cassign_stmt::emit(std::ofstream &of, int level) const
+void vhdl_cassign_stmt::emit(std::ostream &of, int level) const
 {
    lhs_->emit(of, level);
    of << " <= ";
@@ -617,7 +617,7 @@ void vhdl_cassign_stmt::emit(std::ofstream &of, int level) const
    of << ";";
 }
 
-void vhdl_assert_stmt::emit(std::ofstream &of, int level) const
+void vhdl_assert_stmt::emit(std::ostream &of, int level) const
 {
    of << "assert false";  // TODO: Allow arbitrary expression 
    of << " report \"" << reason_ << "\" severity failure;";
@@ -635,7 +635,7 @@ vhdl_if_stmt::~vhdl_if_stmt()
    delete test_;
 }
 
-void vhdl_if_stmt::emit(std::ofstream &of, int level) const
+void vhdl_if_stmt::emit(std::ostream &of, int level) const
 {
    of << "if ";
    test_->emit(of, level);
@@ -653,7 +653,7 @@ vhdl_unaryop_expr::~vhdl_unaryop_expr()
    delete operand_;
 }
 
-void vhdl_unaryop_expr::emit(std::ofstream &of, int level) const
+void vhdl_unaryop_expr::emit(std::ostream &of, int level) const
 {
    switch (op_) {
    case VHDL_UNARYOP_NOT:
@@ -681,7 +681,7 @@ void vhdl_binop_expr::add_expr(vhdl_expr *e)
    operands_.push_back(e);
 }
 
-void vhdl_binop_expr::emit(std::ofstream &of, int level) const
+void vhdl_binop_expr::emit(std::ostream &of, int level) const
 {
    // Expressions are fully parenthesized to remove any
    // ambiguity in the output
@@ -711,7 +711,7 @@ vhdl_case_branch::~vhdl_case_branch()
    delete when_;
 }
 
-void vhdl_case_branch::emit(std::ofstream &of, int level) const
+void vhdl_case_branch::emit(std::ostream &of, int level) const
 {
    of << "when ";
    when_->emit(of, level);
@@ -724,7 +724,7 @@ vhdl_case_stmt::~vhdl_case_stmt()
    delete test_;
 }
 
-void vhdl_case_stmt::emit(std::ofstream &of, int level) const
+void vhdl_case_stmt::emit(std::ostream &of, int level) const
 {
    of << "case ";
    test_->emit(of, level);
@@ -743,7 +743,7 @@ vhdl_while_stmt::~vhdl_while_stmt()
    delete test_;
 }
 
-void vhdl_while_stmt::emit(std::ofstream &of, int level) const
+void vhdl_while_stmt::emit(std::ostream &of, int level) const
 {
    of << "while ";
    test_->emit(of, level);
@@ -762,7 +762,7 @@ vhdl_function::vhdl_function(const char *name, vhdl_type *ret_type)
    variables_.set_parent(&scope_);
 }
 
-void vhdl_function::emit(std::ofstream &of, int level) const
+void vhdl_function::emit(std::ostream &of, int level) const
 {
    of << "function " << name_ << " (";
    emit_children<vhdl_decl>(of, scope_.get_decls(), level, ";");
@@ -777,7 +777,7 @@ void vhdl_function::emit(std::ofstream &of, int level) const
    of << "end function;";
 }
 
-void vhdl_param_decl::emit(std::ofstream &of, int level) const
+void vhdl_param_decl::emit(std::ostream &of, int level) const
 {
    of << name_ << " : ";
    type_->emit(of, level);
diff --git a/tgt-vhdl/vhdl_syntax.hh b/tgt-vhdl/vhdl_syntax.hh
index 16cf8109a..2487840ed 100644
--- a/tgt-vhdl/vhdl_syntax.hh
+++ b/tgt-vhdl/vhdl_syntax.hh
@@ -54,7 +54,7 @@ public:
       : vhdl_expr(type), name_(name), slice_(slice) {}
    ~vhdl_var_ref();
    
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
    const std::string &get_name() const { return name_; }
    void set_slice(vhdl_expr *s) { slice_ = s; }
 private:
@@ -93,7 +93,7 @@ public:
    ~vhdl_binop_expr();
 
    void add_expr(vhdl_expr *e);
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    std::list<vhdl_expr*> operands_;
    vhdl_binop_t op_;
@@ -111,7 +111,7 @@ public:
       : vhdl_expr(type), op_(op), operand_(operand) {}
    ~vhdl_unaryop_expr();
 
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    vhdl_unaryop_t op_;
    vhdl_expr *operand_;
@@ -123,7 +123,7 @@ public:
    vhdl_const_string(const char *value)
       : vhdl_expr(vhdl_type::string(), true), value_(value) {}
 
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    std::string value_;
 };
@@ -131,7 +131,7 @@ private:
 class vhdl_const_bits : public vhdl_expr {
 public:
    vhdl_const_bits(const char *value, int width, bool issigned);
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
    const std::string &get_value() const { return value_; }
    vhdl_expr *cast(const vhdl_type *to);
 private:
@@ -143,7 +143,7 @@ class vhdl_const_bit : public vhdl_expr {
 public:
    vhdl_const_bit(char bit)
       : vhdl_expr(vhdl_type::std_logic(), true), bit_(bit) {}
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    char bit_;
 };
@@ -156,7 +156,7 @@ class vhdl_const_time : public vhdl_expr {
 public:
    vhdl_const_time(int64_t value, time_unit_t units)
       : vhdl_expr(vhdl_type::time(), true), value_(value), units_(units) {}
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    int64_t value_;
    time_unit_t units_;
@@ -166,7 +166,7 @@ class vhdl_const_int : public vhdl_expr {
 public:
    vhdl_const_int(int64_t value)
       : vhdl_expr(vhdl_type::integer(), true), value_(value) {}
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    int64_t value_;
 };
@@ -175,7 +175,7 @@ class vhdl_expr_list : public vhdl_element {
 public:
    ~vhdl_expr_list();
    
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
    bool empty() const { return exprs_.empty(); }
    void add_expr(vhdl_expr *e);
 private:
@@ -193,7 +193,7 @@ public:
    ~vhdl_fcall() {}
 
    void add_expr(vhdl_expr *e) { exprs_.add_expr(e); }
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    std::string name_;
    vhdl_expr_list exprs_;
@@ -219,7 +219,7 @@ public:
       : lhs_(lhs), rhs_(rhs) {}
    ~vhdl_cassign_stmt();
 
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    vhdl_var_ref *lhs_;
    vhdl_expr *rhs_;
@@ -243,7 +243,7 @@ public:
    ~stmt_container();
    
    void add_stmt(vhdl_seq_stmt *stmt);
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
    bool empty() const { return stmts_.empty(); }
 private:
    std::list<vhdl_seq_stmt*> stmts_;
@@ -275,7 +275,7 @@ public:
    vhdl_nbassign_stmt(vhdl_var_ref *lhs, vhdl_expr *rhs)
       : vhdl_abstract_assign_stmt(lhs, rhs) {}
    
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 };
 
 
@@ -284,7 +284,7 @@ public:
    vhdl_assign_stmt(vhdl_var_ref *lhs, vhdl_expr *rhs)
       : vhdl_abstract_assign_stmt(lhs, rhs) {}
 
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 };
 
 
@@ -304,7 +304,7 @@ public:
       : type_(type), expr_(expr) {}
    ~vhdl_wait_stmt();
    
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    vhdl_wait_type_t type_;
    vhdl_expr *expr_;
@@ -313,7 +313,7 @@ private:
 
 class vhdl_null_stmt : public vhdl_seq_stmt {
 public:
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 };
 
 
@@ -322,7 +322,7 @@ public:
    vhdl_assert_stmt(const char *reason)
       : reason_(reason) {}
 
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    std::string reason_;
 };
@@ -335,7 +335,7 @@ public:
 
    stmt_container *get_then_container() { return &then_part_; }
    stmt_container *get_else_container() { return &else_part_; }
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    vhdl_expr *test_;
    stmt_container then_part_, else_part_;
@@ -352,7 +352,7 @@ public:
    ~vhdl_case_branch();
 
    stmt_container *get_container() { return &stmts_; }
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    vhdl_expr *when_;
    stmt_container stmts_;
@@ -366,7 +366,7 @@ public:
    ~vhdl_case_stmt();
 
    void add_branch(vhdl_case_branch *b) { branches_.push_back(b); }
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    vhdl_expr *test_;
    case_branch_list_t branches_;
@@ -379,7 +379,7 @@ public:
    ~vhdl_while_stmt();
 
    stmt_container *get_container() { return &stmts_; }
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    vhdl_expr *test_;
    stmt_container stmts_;
@@ -394,7 +394,7 @@ class vhdl_pcall_stmt : public vhdl_seq_stmt {
 public:
    vhdl_pcall_stmt(const char *name) : name_(name) {}
    
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
    void add_expr(vhdl_expr *e) { exprs_.add_expr(e); }
 private:
    std::string name_;
@@ -438,7 +438,7 @@ class vhdl_component_decl : public vhdl_decl {
 public:
    static vhdl_component_decl *component_decl_for(vhdl_entity *ent);
 
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    vhdl_component_decl(const char *name);
 
@@ -454,7 +454,7 @@ class vhdl_var_decl : public vhdl_decl {
 public:
    vhdl_var_decl(const char *name, vhdl_type *type)
       : vhdl_decl(name, type) {}
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 };
 
 
@@ -465,7 +465,7 @@ class vhdl_signal_decl : public vhdl_decl {
 public:
    vhdl_signal_decl(const char *name, vhdl_type *type)
       : vhdl_decl(name, type) {}
-   virtual void emit(std::ofstream &of, int level) const;
+   virtual void emit(std::ostream &of, int level) const;
 };
 
 
@@ -476,7 +476,7 @@ class vhdl_param_decl : public vhdl_decl {
 public:
    vhdl_param_decl(const char *name, vhdl_type *type)
       : vhdl_decl(name, type) {}
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 };
 
 enum vhdl_port_mode_t {
@@ -496,7 +496,7 @@ public:
                   vhdl_port_mode_t mode)
       : vhdl_decl(name, type), mode_(mode) {}
 
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
 private:
    vhdl_port_mode_t mode_;
 };
@@ -520,7 +520,7 @@ public:
    vhdl_comp_inst(const char *inst_name, const char *comp_name);
    ~vhdl_comp_inst();
 
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
    void map_port(const char *name, vhdl_expr *expr);
 private:
    std::string comp_name_, inst_name_;
@@ -580,7 +580,7 @@ class vhdl_function : public vhdl_decl, public vhdl_procedural {
 public:
    vhdl_function(const char *name, vhdl_type *ret_type);
    
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
    vhdl_scope *get_scope() { return &variables_; }
    void add_param(vhdl_param_decl *p) { scope_.add_decl(p); }
 private:
@@ -592,7 +592,7 @@ class vhdl_process : public vhdl_conc_stmt, public vhdl_procedural {
 public:
    vhdl_process(const char *name = "") : name_(name) {}
 
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
    void add_sensitivity(const char *name);
 private:
    std::string name_;
@@ -609,7 +609,7 @@ public:
       : name_(name), entity_(entity) {}
    virtual ~vhdl_arch();
 
-   void emit(std::ofstream &of, int level=0) const;
+   void emit(std::ostream &of, int level=0) const;
    void add_stmt(vhdl_process *proc);
    void add_stmt(vhdl_conc_stmt *stmt);
    vhdl_scope *get_scope() { return &scope_; }
@@ -631,7 +631,7 @@ public:
                vhdl_arch *arch);
    virtual ~vhdl_entity();
 
-   void emit(std::ofstream &of, int level=0) const;
+   void emit(std::ostream &of, int level=0) const;
    void add_port(vhdl_port_decl *decl);
    vhdl_arch *get_arch() const { return arch_; }
    const std::string &get_name() const { return name_; }
diff --git a/tgt-vhdl/vhdl_type.cc b/tgt-vhdl/vhdl_type.cc
index 4176cfce4..77b3a7b0f 100644
--- a/tgt-vhdl/vhdl_type.cc
+++ b/tgt-vhdl/vhdl_type.cc
@@ -112,7 +112,7 @@ std::string vhdl_type::get_decl_string() const
    }
 }
 
-void vhdl_type::emit(std::ofstream &of, int level) const
+void vhdl_type::emit(std::ostream &of, int level) const
 {
    of << get_decl_string();
 }
diff --git a/tgt-vhdl/vhdl_type.hh b/tgt-vhdl/vhdl_type.hh
index e4e41d3e2..b0e0c6f3b 100644
--- a/tgt-vhdl/vhdl_type.hh
+++ b/tgt-vhdl/vhdl_type.hh
@@ -47,7 +47,7 @@ public:
       : name_(name), msb_(msb), lsb_(lsb) {}
    virtual ~vhdl_type() {}
 
-   void emit(std::ofstream &of, int level) const;
+   void emit(std::ostream &of, int level) const;
    vhdl_type_name_t get_name() const { return name_; }
    std::string get_string() const;
    std::string get_decl_string() const;