diff --git a/platforms/app/main.c b/platforms/app/main.c
index 906ca88..1701cc8 100644
--- a/platforms/app/main.c
+++ b/platforms/app/main.c
@@ -55,9 +55,6 @@ M3Result repl_call  (IM3Runtime runtime, const char* name, int argc, const char*
         if (!strcmp(name, "main") || !strcmp(name, "_main")) {
             return "passing arguments to libc main() not implemented";
         }
-//        else if (!strcmp(name, "_start")) {
-//            return "passing arguments to wasi _start() not implemented";
-//        }
     }
 
     result = m3_CallWithArgs (func, argc, argv);
@@ -176,7 +173,12 @@ int  main  (int i_argc, const char* i_argv[])
         if (result) FATAL("m3_LinkLibC: %s", result);
 
         if (argFunc and not argRepl) {
-            result = repl_call(runtime, argFunc, i_argc, i_argv);
+            if (!strcmp(argFunc, "_start")) {
+                // When passing args to WASI, include wasm filename as argv[0]
+                result = repl_call(runtime, argFunc, i_argc+1, i_argv-1);
+            } else {
+                result = repl_call(runtime, argFunc, i_argc, i_argv);
+            }
             if (result) FATAL("repl_call: %s", result);
         }
     }
@@ -209,24 +211,23 @@ int  main  (int i_argc, const char* i_argv[])
         }
 
         if (result) {
-            printf ("Error: %s", result);
+            fprintf (stderr, "Error: %s", result);
             M3ErrorInfo info = m3_GetErrorInfo (runtime);
-            printf (" (%s)\n", info.message);
+            fprintf (stderr, " (%s)\n", info.message);
         }
     }
 
 _onfatal:
     if (result) {
-        printf ("Error: %s", result);
+        fprintf (stderr, "Error: %s", result);
         if (runtime)
         {
             M3ErrorInfo info = m3_GetErrorInfo (runtime);
-            printf (" (%s)", info.message);
+            fprintf (stderr, " (%s)", info.message);
         }
+        fprintf (stderr, "\n");
     }
 
-    printf ("\n");
-
     m3_FreeEnvironment (env);
     
     return 0;
diff --git a/source/m3_env.c b/source/m3_env.c
index 01f60c2..25027bc 100644
--- a/source/m3_env.c
+++ b/source/m3_env.c
@@ -584,30 +584,30 @@ _       ((M3Result)Call (i_function->compiled, stack, linearMemory, d_m3OpDefaul
 
 #if d_m3LogOutput
         switch (ftype->returnType) {
-        case c_m3Type_none: printf("Result: <Empty Stack>\n"); break;
+        case c_m3Type_none: fprintf (stderr, "Result: <Empty Stack>\n"); break;
 #ifdef USE_HUMAN_FRIENDLY_ARGS
-        case c_m3Type_i32:  printf("Result: %" PRIi32 "\n", *(i32*)(stack));  break;
-        case c_m3Type_i64:  printf("Result: %" PRIi64 "\n", *(i64*)(stack));  break;
-        case c_m3Type_f32:  printf("Result: %f\n",   *(f32*)(stack));  break;
-        case c_m3Type_f64:  printf("Result: %lf\n",  *(f64*)(stack));  break;
+        case c_m3Type_i32:  fprintf (stderr, "Result: %" PRIi32 "\n", *(i32*)(stack));  break;
+        case c_m3Type_i64:  fprintf (stderr, "Result: %" PRIi64 "\n", *(i64*)(stack));  break;
+        case c_m3Type_f32:  fprintf (stderr, "Result: %f\n",   *(f32*)(stack));  break;
+        case c_m3Type_f64:  fprintf (stderr, "Result: %lf\n",  *(f64*)(stack));  break;
 #else
-        case c_m3Type_i32:  printf("Result: %u\n",  *(u32*)(stack));  break;
+        case c_m3Type_i32:  fprintf (stderr, "Result: %u\n",  *(u32*)(stack));  break;
         case c_m3Type_f32:  {
             union { u32 u; f32 f; } union32;
             union32.f = * (f32 *)(stack);
-            printf("Result: %u\n", union32.u );
+            fprintf (stderr, "Result: %u\n", union32.u );
             break;
         }
         case c_m3Type_i64:
         case c_m3Type_f64:
-            printf("Result: %" PRIu64 "\n", *(u64*)(stack));  break;
+            fprintf (stderr, "Result: %" PRIu64 "\n", *(u64*)(stack));  break;
 #endif // USE_HUMAN_FRIENDLY_ARGS
         default: _throw("unknown return type");
         }
 
 #if d_m3LogNativeStack
         size_t stackUsed =  m3StackGetMax();
-        printf("Native stack used: %d\n", stackUsed);
+        fprintf (stderr, "Native stack used: %d\n", stackUsed);
 #endif // d_m3LogNativeStack
 
 #endif // d_m3LogOutput