diff --git a/rtl/watcom/system.pp b/rtl/watcom/system.pp
index f23f2e2542..731b1c4c93 100644
--- a/rtl/watcom/system.pp
+++ b/rtl/watcom/system.pp
@@ -24,6 +24,9 @@ INTERFACE
 {$define FPC_ANSI_TEXTFILEREC}
 { include system-independent routine headers }
 
+{ wasm does not support SSE3 instructions }
+{$define FASTMOVE_DISABLE_SSE3}
+
 {$include systemh.inc}