diff --git a/libsigrok.h b/libsigrok.h
index 2232071c..985473c6 100644
--- a/libsigrok.h
+++ b/libsigrok.h
@@ -73,6 +73,7 @@ enum {
 	SR_ERR_NA         = -6, /**< Not applicable. */
 	SR_ERR_DEV_CLOSED = -7, /**< Device is closed, but needs to be open. */
 	SR_ERR_TIMEOUT    = -8, /**< A timeout occurred. */
+	SR_ERR_PROBE_GROUP= -9, /**< A probe group must be specified. */
 
 	/*
 	 * Note: When adding entries here, don't forget to also update the