diff --git a/tgt-vvp/draw_ufunc.c b/tgt-vvp/draw_ufunc.c
index 477ddfab8..7fe88abf2 100644
--- a/tgt-vvp/draw_ufunc.c
+++ b/tgt-vvp/draw_ufunc.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005-2015 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 2005-2016 Stephen Williams (steve@icarus.com)
  *
  *    This source code is free software; you can redistribute it
  *    and/or modify it in source code form under the terms of the GNU
@@ -187,6 +187,7 @@ void draw_ufunc_vec4(ivl_expr_t expr)
 {
       ivl_scope_t def = ivl_expr_def(expr);
       ivl_signal_t retval = ivl_scope_port(def, 0);
+      (void) retval;
 
 	/* Take in arguments to function and call function code. */
       draw_ufunc_preamble(expr);
@@ -198,6 +199,7 @@ void draw_ufunc_real(ivl_expr_t expr)
 {
       ivl_scope_t def = ivl_expr_def(expr);
       ivl_signal_t retval = ivl_scope_port(def, 0);
+      (void) retval;
 
 	/* Take in arguments to function and call the function code. */
       draw_ufunc_preamble(expr);
diff --git a/vvp/vthread.cc b/vvp/vthread.cc
index c341fc707..e99206198 100644
--- a/vvp/vthread.cc
+++ b/vvp/vthread.cc
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001-2015 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 2001-2016 Stephen Williams (steve@icarus.com)
  *
  *    This source code is free software; you can redistribute it
  *    and/or modify it in source code form under the terms of the GNU
@@ -4985,7 +4985,7 @@ bool of_RET_REAL(vthread_t thr, vvp_code_t cp)
 	    assert(fun_thr->parent);
 	    fun_thr = fun_thr->parent;
       }
-      assert(index >= 0 && index < fun_thr->args_real.size());
+      assert(index < fun_thr->args_real.size());
       unsigned depth = fun_thr->args_real[index];
 	// Use the depth to put the value into the stack of
 	// the parent thread.
@@ -5007,7 +5007,7 @@ bool of_RET_VEC4(vthread_t thr, vvp_code_t cp)
 	    assert(fun_thr->parent);
 	    fun_thr = fun_thr->parent;
       }
-      assert(index >= 0 && index < fun_thr->args_vec4.size());
+      assert(index < fun_thr->args_vec4.size());
       unsigned depth = fun_thr->args_vec4[index];
 
       int off = off_index? thr->words[off_index].w_int : 0;
@@ -5077,7 +5077,7 @@ bool of_RETLOAD_REAL(vthread_t thr, vvp_code_t cp)
 	    assert(fun_thr->parent);
 	    fun_thr = fun_thr->parent;
       }
-      assert(index >= 0 && index < fun_thr->args_real.size());
+      assert(index < fun_thr->args_real.size());
       unsigned depth = fun_thr->args_real[index];
 	// Use the depth to extract the values from the stack
 	// of the parent thread.
@@ -5097,7 +5097,7 @@ bool of_RETLOAD_VEC4(vthread_t thr, vvp_code_t cp)
 	    assert(fun_thr->parent);
 	    fun_thr = fun_thr->parent;
       }
-      assert(index >= 0 && index < fun_thr->args_vec4.size());
+      assert(index < fun_thr->args_vec4.size());
       unsigned depth = fun_thr->args_vec4[index];
 	// Use the depth to put the value into the stack of
 	// the parent thread.