diff --git a/python/fusion_engine_client/messages/defs.py b/python/fusion_engine_client/messages/defs.py
index 96cae695..7829fa03 100644
--- a/python/fusion_engine_client/messages/defs.py
+++ b/python/fusion_engine_client/messages/defs.py
@@ -233,7 +233,12 @@ class SourceIdentifier(IntEnum):
     # 300 - 399 is reserved for GNSS receivers/antennae.
     PRIMARY_GNSS_ANTENNA = 300
     SECONDARY_GNSS_ANTENNA = 301
+    # 400 - 499 is reserved for wheel speeds.
     # 500 - 599 is reserved for external pose sources, such as an external SLAM or VIO/LIO.
+    # 600 - 699 is reserved for redundant/secondary processing engines. The ranges above identify the sensor or vehicle
+    # location that the data corresponds to. These instead identify *which device/process produced a message*.
+    PRIMARY_PROCESSING_ENGINE = 600
+    SECONDARY_PROCESSING_ENGINE = 601
     ## Invalid source identifier.
     INVALID = 0xFFFFFFFF
 
diff --git a/src/point_one/fusion_engine/messages/defs.h b/src/point_one/fusion_engine/messages/defs.h
index f988c8b2..27a4ac10 100644
--- a/src/point_one/fusion_engine/messages/defs.h
+++ b/src/point_one/fusion_engine/messages/defs.h
@@ -607,8 +607,20 @@ enum class SourceIdentifier : uint32_t {
    */
   SECONDARY_GNSS_ANTENNA = 301,
 
+  // 400 - 499 is reserved for wheel speeds.
+
   // 500 - 599 is reserved for external pose sources, such as an external SLAM
   // or VIO/LIO.
+
+  // 600 - 699 is reserved for redundant/secondary processing engines. The
+  // ranges above identify the sensor or vehicle location that the data
+  // corresponds to. These instead identify *which device/process produced a
+  // message*.
+  /** The primary processing engine. */
+  PRIMARY_PROCESSING_ENGINE = 600,
+  /** A redundant/secondary processing engine. */
+  SECONDARY_PROCESSING_ENGINE = 601,
+
   /** Invalid source identifier. */
   INVALID = 0xFFFFFFFF,
 };