diff --git a/src/mesa/drivers/dri/r300/compiler/r300_fragprog_emit.c b/src/mesa/drivers/dri/r300/compiler/r300_fragprog_emit.c
index 3b2b06fc2bd..9f19f8fe660 100644
--- a/src/mesa/drivers/dri/r300/compiler/r300_fragprog_emit.c
+++ b/src/mesa/drivers/dri/r300/compiler/r300_fragprog_emit.c
@@ -76,6 +76,9 @@ static void use_temporary(struct r300_fragment_program_code *code, unsigned int
 
 static unsigned int use_source(struct r300_fragment_program_code* code, struct radeon_pair_instruction_source src)
 {
+	if (!src.Used)
+		return 0;
+
 	if (src.File == RC_FILE_CONSTANT) {
 		return src.Index | (1 << 5);
 	} else if (src.File == RC_FILE_TEMPORARY) {
diff --git a/src/mesa/drivers/dri/r300/compiler/r500_fragprog_emit.c b/src/mesa/drivers/dri/r300/compiler/r500_fragprog_emit.c
index efa3bb5b473..abbf704533b 100644
--- a/src/mesa/drivers/dri/r300/compiler/r500_fragprog_emit.c
+++ b/src/mesa/drivers/dri/r300/compiler/r500_fragprog_emit.c
@@ -200,6 +200,9 @@ static void use_temporary(struct r500_fragment_program_code* code, unsigned int
 
 static unsigned int use_source(struct r500_fragment_program_code* code, struct radeon_pair_instruction_source src)
 {
+	if (!src.Used)
+		return 0;
+
 	if (src.File == RC_FILE_CONSTANT) {
 		return src.Index | 0x100;
 	} else if (src.File == RC_FILE_TEMPORARY) {