diff --git a/cgen/sim-decode.scm b/cgen/sim-decode.scm
index 0c6d48c..42c41ec 100644
--- a/cgen/sim-decode.scm
+++ b/cgen/sim-decode.scm
@@ -437,7 +437,10 @@ void
        (string-append
 	"    CGEN_INSN_WORD insn = "
 	(if (adata-integral-insn? CURRENT-ARCH)
-	    "entire_insn;\n"
+	    (if (current-arch-insn-lsb0?)
+	      "entire_insn;\n"
+	      (string-append
+	        "entire_insn >> (sizeof(UINT) * 8 - " (number->string (sfmt-length sfmt)) ");\n" ))
 	    "base_insn;\n"))
        "")
    (gen-define-field-macro sfmt)