diff --git a/tgt-vhdl/cast.cc b/tgt-vhdl/cast.cc
index 230108b12..22f6b89f4 100644
--- a/tgt-vhdl/cast.cc
+++ b/tgt-vhdl/cast.cc
@@ -1,7 +1,7 @@
 /*
  *  Generate code to convert between VHDL types.
  *
- *  Copyright (C) 2008  Nick Gasson (nick@nickg.me.uk)
+ *  Copyright (C) 2008-2009  Nick Gasson (nick@nickg.me.uk)
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -60,6 +60,8 @@ vhdl_expr *vhdl_expr::cast(const vhdl_type *to)
          assert(false);
       }
    }
+   assert(false);
+   return NULL;
 }
 
 /*
@@ -140,9 +142,8 @@ vhdl_expr *vhdl_expr::to_boolean()
       conv->add_expr(this);
       return conv;
    }
-   else {
-      assert(false);
-   }
+   assert(false);
+   return NULL;
 }
 
 /*
@@ -180,8 +181,8 @@ vhdl_expr *vhdl_expr::to_std_logic()
 
       return ah;
    }
-   else
-      assert(false);
+   assert(false);
+   return NULL;
 }
 
 /*
@@ -274,8 +275,8 @@ vhdl_expr *vhdl_const_bits::to_vector(vhdl_type_name_t name, int w)
       value_.resize(w, sign_bit());  
       return this;
    }
-   else
-      assert(false);
+   assert(false);
+   return NULL;
 }
 
 vhdl_expr *vhdl_const_bits::to_integer()
diff --git a/tgt-vhdl/state.cc b/tgt-vhdl/state.cc
index 7acab014c..0ced93f27 100644
--- a/tgt-vhdl/state.cc
+++ b/tgt-vhdl/state.cc
@@ -139,6 +139,7 @@ ivl_signal_t find_signal_named(const std::string &name, const vhdl_scope *scope)
          return (*it).first;
    }
    assert(false);
+   return NULL;
 }
 
 // Compare the name of an entity against a string
diff --git a/tgt-vhdl/stmt.cc b/tgt-vhdl/stmt.cc
index d5f94c1e5..774ce9d06 100644
--- a/tgt-vhdl/stmt.cc
+++ b/tgt-vhdl/stmt.cc
@@ -239,9 +239,9 @@ assign_for(vhdl_decl::assign_type_t atype, vhdl_var_ref *lhs, vhdl_expr *rhs)
       return new vhdl_assign_stmt(lhs, rhs);
    case vhdl_decl::ASSIGN_NONBLOCK:
       return new vhdl_nbassign_stmt(lhs, rhs);
-   default:
-      assert(false);
    }   
+   assert(false);
+   return NULL;
 }
 
 /*
diff --git a/tgt-vhdl/support.cc b/tgt-vhdl/support.cc
index 01eb16869..5001d5bc8 100644
--- a/tgt-vhdl/support.cc
+++ b/tgt-vhdl/support.cc
@@ -1,7 +1,7 @@
 /*
  *  Support functions for VHDL output.
  *
- *  Copyright (C) 2008  Nick Gasson (nick@nickg.me.uk)
+ *  Copyright (C) 2008-2009  Nick Gasson (nick@nickg.me.uk)
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -51,6 +51,7 @@ const char *support_function::function_name(support_function_t type)
    default:
       assert(false);
    }
+   return "Invalid";
 }
 
 vhdl_type *support_function::function_type(support_function_t type)
@@ -74,9 +75,9 @@ vhdl_type *support_function::function_type(support_function_t type)
       return new vhdl_type(VHDL_TYPE_UNSIGNED);
    case SF_LOGIC_TO_INTEGER:
       return vhdl_type::integer();
-   default:
-      assert(false);
    }
+   assert(false);
+   return vhdl_type::boolean();
 }
 
 void support_function::emit_ternary(std::ostream &of, int level) const
diff --git a/tgt-vhdl/vhdl_syntax.hh b/tgt-vhdl/vhdl_syntax.hh
index 326f70084..d1a278aae 100644
--- a/tgt-vhdl/vhdl_syntax.hh
+++ b/tgt-vhdl/vhdl_syntax.hh
@@ -571,7 +571,8 @@ public:
    // For some sorts of declarations it doesn't make sense
    // to assign to it so calling assignment_type just raises
    // an assertion failure
-   virtual assign_type_t assignment_type() const { assert(false); }
+   virtual assign_type_t assignment_type() const { assert(false);
+                                                   return ASSIGN_BLOCK; }
 
    // True if this declaration can be read from
    virtual bool is_readable() const { return true; }