diff --git a/assemble.c b/assemble.c
index 6fb5de91..99b833ce 100644
--- a/assemble.c
+++ b/assemble.c
@@ -1152,7 +1152,7 @@ static int64_t calcsize(int32_t segment, int64_t offset, int bits,
             errfunc(ERR_NONFATAL, "invalid operands in non-64-bit mode");
             return -1;
         }
-        if (ins->vex_cm != 1 || (ins->rex & (REX_W|REX_R|REX_B)))
+        if (ins->vex_cm != 1 || (ins->rex & (REX_W|REX_X|REX_B)))
             length += 3;
         else
             length += 2;
diff --git a/test/br3109604.asm b/test/br3109604.asm
new file mode 100644
index 00000000..9032e8d5
--- /dev/null
+++ b/test/br3109604.asm
@@ -0,0 +1,9 @@
+;Testname=unoptimized; Arguments=-O0 -fbin -obr3109604.bin; Files=stdout stderr br3109604.bin
+;Testname=optimized;   Arguments=-Ox -fbin -obr3109604.bin; Files=stdout stderr br3109604.bin
+
+	bits 64
+b0:	vmovd xmm2, [rdx+r9]
+e0:	
+	
+	section .data
+len:	dd e0 - b0		; Should be 6