diff --git a/src/gallium/auxiliary/tgsi/tgsi_scan.c b/src/gallium/auxiliary/tgsi/tgsi_scan.c
index 7523baf4ce0..98a5fec7716 100644
--- a/src/gallium/auxiliary/tgsi/tgsi_scan.c
+++ b/src/gallium/auxiliary/tgsi/tgsi_scan.c
@@ -258,6 +258,9 @@ tgsi_scan_shader(const struct tgsi_token *tokens,
                   info->output_semantic_index[reg] = (ubyte) semIndex;
                   info->num_outputs++;
 
+                  if (semName == TGSI_SEMANTIC_COLOR)
+                     info->colors_written |= 1 << semIndex;
+
                   if (procType == TGSI_PROCESSOR_VERTEX ||
                       procType == TGSI_PROCESSOR_GEOMETRY ||
                       procType == TGSI_PROCESSOR_TESS_CTRL ||
diff --git a/src/gallium/auxiliary/tgsi/tgsi_scan.h b/src/gallium/auxiliary/tgsi/tgsi_scan.h
index b81bdd71f14..6301f91c1ec 100644
--- a/src/gallium/auxiliary/tgsi/tgsi_scan.h
+++ b/src/gallium/auxiliary/tgsi/tgsi_scan.h
@@ -76,6 +76,7 @@ struct tgsi_shader_info
 
    uint opcode_count[TGSI_OPCODE_LAST];  /**< opcode histogram */
 
+   ubyte colors_written;
    boolean reads_position; /**< does fragment shader read position? */
    boolean reads_z; /**< does fragment shader read depth? */
    boolean writes_z;  /**< does fragment shader write Z value? */