diff --git a/include/rlbox_stdlib.hpp b/include/rlbox_stdlib.hpp
--- a/include/rlbox_stdlib.hpp
+++ b/include/rlbox_stdlib.hpp
@@ -173,11 +173,13 @@ inline T_Wrap<T_Rhs*, T_Sbx> memcpy(rlbo
   void* dest_start = dest_tainted.INTERNAL_unverified_safe();
   detail::check_range_doesnt_cross_app_sbx_boundary<T_Sbx>(dest_start, num_val);
 
-  // src also needs to be checked, as we don't want to allow a src rand to start
-  // inside the sandbox and end outside, and vice versa
   // src may or may not be a wrapper, so use unwrap_value
   const void* src_start = detail::unwrap_value(src);
-  detail::check_range_doesnt_cross_app_sbx_boundary<T_Sbx>(src_start, num_val);
+
+  // if src is also a tainted/tainted-volatile pointer apply the same check
+  if constexpr(detail::rlbox_is_tainted_or_vol_v<T_Lhs>) {
+    detail::check_range_doesnt_cross_app_sbx_boundary<T_Sbx>(src_start, num_val);
+  }
 
   std::memcpy(dest_start, src_start, num_val);
 
@@ -205,11 +207,13 @@ inline tainted_int_hint memcmp(rlbox_san
   void* dest_start = dest.INTERNAL_unverified_safe();
   detail::check_range_doesnt_cross_app_sbx_boundary<T_Sbx>(dest_start, num_val);
 
-  // src also needs to be checked, as we don't want to allow a src rand to start
-  // inside the sandbox and end outside, and vice versa
   // src may or may not be a wrapper, so use unwrap_value
   const void* src_start = detail::unwrap_value(src);
-  detail::check_range_doesnt_cross_app_sbx_boundary<T_Sbx>(src_start, num_val);
+
+  // if src is also a tainted/tainted-volatile pointer apply the same check
+  if constexpr(detail::rlbox_is_tainted_or_vol_v<T_Lhs>) {
+    detail::check_range_doesnt_cross_app_sbx_boundary<T_Sbx>(src_start, num_val);
+  }
 
   int ret = std::memcmp(dest_start, src_start, num_val);
   tainted_int_hint converted_ret(ret);
@@ -243,6 +247,10 @@ tainted<T*, T_Sbx> copy_memory_or_grant_
                 "copy_memory_or_grant_access not supported on this type as "
                 "there may be ABI differences");
 
+  static_assert(!detail::rlbox_is_tainted_or_vol_v<T>,
+                "copy_memory_or_grant_access called on tainted type. Tainted "
+                "data is already accessible to the sandbox. ");
+
   // overflow ok
   size_t source_size = num * sizeof(T);