diff --git a/src/mesa/drivers/dri/r300/compiler/radeon_optimize.c b/src/mesa/drivers/dri/r300/compiler/radeon_optimize.c
index c15a9b1..d055930 100644
--- a/src/mesa/drivers/dri/r300/compiler/radeon_optimize.c
+++ b/src/mesa/drivers/dri/r300/compiler/radeon_optimize.c
@@ -626,6 +626,21 @@ static void presub_replace_add(struct peephole_state *s,
 	inst->U.I.SrcReg[src_index].Index = presub_opcode;
 }
 
+static int is_presub_candidate(struct rc_instruction * inst)
+{
+	const struct rc_opcode_info * info = rc_get_opcode_info(inst->U.I.Opcode);
+	unsigned int i;
+
+	if (inst->U.I.PreSub.Opcode != RC_PRESUB_NONE || inst->U.I.SaturateMode)
+		return 0;
+
+	for(i = 0; i < info->NumSrcRegs; i++) {
+		if (src_reads_dst_mask(inst->U.I.SrcReg[i], inst->U.I.DstReg))
+			return 0;
+	}
+	return 1;
+}
+
 static int peephole_add_presub_add(
 	struct radeon_compiler * c,
 	struct rc_instruction * inst_add)
@@ -635,10 +650,7 @@ static int peephole_add_presub_add(
 	unsigned int i;
 	struct peephole_state s;
 
-	if (inst_add->U.I.PreSub.Opcode != RC_PRESUB_NONE)
-		return 0;
-
-	if (inst_add->U.I.SaturateMode)
+	if (!is_presub_candidate(inst_add))
 		return 0;
 
 	if (inst_add->U.I.SrcReg[0].Swizzle != inst_add->U.I.SrcReg[1].Swizzle)
@@ -705,10 +717,7 @@ static int peephole_add_presub_inv(
 	unsigned int i, swz, mask;
 	struct peephole_state s;
 
-	if (inst_add->U.I.PreSub.Opcode != RC_PRESUB_NONE)
-		return 0;
-
-	if (inst_add->U.I.SaturateMode)
+	if (!is_presub_candidate(inst_add))
 		return 0;
 
 	mask = inst_add->U.I.DstReg.WriteMask;