diff --git a/lib/rb/ext/binaryprotocolaccelerated.c b/lib/rb/ext/binaryprotocolaccelerated.c
index 6e295ed..1da7a3d 100644
--- a/lib/rb/ext/binaryprotocolaccelerated.c
+++ b/lib/rb/ext/binaryprotocolaccelerated.c
@@ -186,7 +186,7 @@
 
   spec->type = type;
   
-  if (Qnil != name) {
+  if (!NIL_P(name)) {
     spec->name = StringValuePtr(name);
   } else {
     spec->name = NULL;
@@ -317,6 +317,8 @@
       VALUE keys;
       VALUE key;
       VALUE val;
+
+      Check_Type(value, T_HASH);
       
       keys = rb_funcall(value, keys_id, 0);
       
@@ -347,14 +349,17 @@
     }
     
     case T_LIST: {
+      Check_Type(value, T_ARRAY);
+
       sz = RARRAY(value)->len;
       
       write_list_begin(buf, spec->data.element->type, sz);
       for (i = 0; i < sz; ++i) {
+        VALUE val = rb_ary_entry(value, i);
         if (IS_CONTAINER(spec->data.element->type)) {
-          write_container(buf, rb_ary_entry(value, i), spec->data.element);
+          write_container(buf, val, spec->data.element);
         } else {
-          binary_encoding(buf, rb_ary_entry(value, i), spec->data.element->type);
+          binary_encoding(buf, val, spec->data.element->type);
         }
       }
       write_list_end(buf);
@@ -380,10 +385,11 @@
       write_set_begin(buf, spec->data.element->type, sz);
       
       for (i = 0; i < sz; i++) {
+        VALUE val = rb_ary_entry(items, i);
         if (IS_CONTAINER(spec->data.element->type)) {
-          write_container(buf, rb_ary_entry(items, i), spec->data.element);
+          write_container(buf, val, spec->data.element);
         } else {
-          binary_encoding(buf, rb_ary_entry(items, i), spec->data.element->type);
+          binary_encoding(buf, val, spec->data.element->type);
         }
       }
       
@@ -409,7 +415,7 @@
   
   VALUE value = rb_ivar_get(obj, rb_intern(name_buf));
   
-  if (Qnil == value) {
+  if (NIL_P(value)) {
     free_field_spec(spec);
     return 0;
   }
@@ -471,9 +477,12 @@
       write_double(buf, NUM2DBL(obj));
       break;
 
-    case T_STR:
-      write_string(buf, StringValuePtr(obj), RSTRING(obj)->len);
+    case T_STR: {
+      // make sure to call StringValuePtr before calling RSTRING
+      char *ptr = StringValuePtr(obj);
+      write_string(buf, ptr, RSTRING(obj)->len);
       break;
+    }
           
     case T_STRCT: {
       // rb_hash_foreach has to take args as a ruby array