diff --git a/src/ipa/raspberrypi/controller/rpi/alsc.cpp b/src/ipa/raspberrypi/controller/rpi/alsc.cpp
index 183a0c95..c354c985 100644
--- a/src/ipa/raspberrypi/controller/rpi/alsc.cpp
+++ b/src/ipa/raspberrypi/controller/rpi/alsc.cpp
@@ -146,6 +146,7 @@ void Alsc::Read(boost::property_tree::ptree const &params)
 	config_.threshold = params.get<double>("threshold", 1e-3);
 }
 
+static double get_ct(Metadata *metadata, double default_ct);
 static void get_cal_table(double ct,
 			  std::vector<AlscCalibration> const &calibrations,
 			  double cal_table[XY]);
@@ -210,6 +211,9 @@ void Alsc::SwitchMode(CameraMode const &camera_mode,
 	// change.
 	bool reset_tables = first_time_ || compare_modes(camera_mode_, camera_mode);
 
+	// Believe the colour temperature from the AWB, if there is one.
+	ct_ = get_ct(metadata, ct_);
+
 	// Ensure the other thread isn't running while we do this.
 	waitForAysncThread();
 
@@ -254,7 +258,7 @@ void Alsc::fetchAsyncResults()
 	memcpy(sync_results_, async_results_, sizeof(sync_results_));
 }
 
-static double get_ct(Metadata *metadata, double default_ct)
+double get_ct(Metadata *metadata, double default_ct)
 {
 	AwbStatus awb_status;
 	awb_status.temperature_K = default_ct; // in case nothing found
diff --git a/src/ipa/raspberrypi/controller/rpi/awb.cpp b/src/ipa/raspberrypi/controller/rpi/awb.cpp
index 10600f75..f66c2b29 100644
--- a/src/ipa/raspberrypi/controller/rpi/awb.cpp
+++ b/src/ipa/raspberrypi/controller/rpi/awb.cpp
@@ -19,6 +19,9 @@ using namespace RPiController;
 
 const double Awb::RGB::INVALID = -1.0;
 
+// todo - the locking in this algorithm needs some tidying up as has been done
+// elsewhere (ALSC and AGC).
+
 void AwbMode::Read(boost::property_tree::ptree const &params)
 {
 	ct_lo = params.get<double>("lo");
@@ -121,6 +124,7 @@ Awb::Awb(Controller *controller)
 	async_abort_ = async_start_ = async_started_ = async_finished_ = false;
 	mode_ = nullptr;
 	manual_r_ = manual_b_ = 0.0;
+	first_switch_mode_ = true;
 	async_thread_ = std::thread(std::bind(&Awb::asyncFunc, this));
 }
 
@@ -199,9 +203,19 @@ void Awb::SwitchMode([[maybe_unused]] CameraMode const &camera_mode,
 		prev_sync_results_.gain_r = manual_r_;
 		prev_sync_results_.gain_g = 1.0;
 		prev_sync_results_.gain_b = manual_b_;
+		// If we're starting up for the first time, try and
+		// "dead reckon" the corresponding colour temperature.
+		if (first_switch_mode_ && config_.bayes) {
+			Pwl ct_r_inverse = config_.ct_r.Inverse();
+			Pwl ct_b_inverse = config_.ct_b.Inverse();
+			double ct_r = ct_r_inverse.Eval(ct_r_inverse.Domain().Clip(1 / manual_r_));
+			double ct_b = ct_b_inverse.Eval(ct_b_inverse.Domain().Clip(1 / manual_b_));
+			prev_sync_results_.temperature_K = (ct_r + ct_b) / 2;
+		}
 		sync_results_ = prev_sync_results_;
 	}
 	metadata->Set("awb.status", prev_sync_results_);
+	first_switch_mode_ = false;
 }
 
 void Awb::fetchAsyncResults()
diff --git a/src/ipa/raspberrypi/controller/rpi/awb.hpp b/src/ipa/raspberrypi/controller/rpi/awb.hpp
index 6fc045ce..83b81498 100644
--- a/src/ipa/raspberrypi/controller/rpi/awb.hpp
+++ b/src/ipa/raspberrypi/controller/rpi/awb.hpp
@@ -159,6 +159,7 @@ private:
 	double manual_r_;
 	// manual b setting
 	double manual_b_;
+	bool first_switch_mode_; // is this the first call to SwitchMode?
 };
 
 static inline Awb::RGB operator+(Awb::RGB const &a, Awb::RGB const &b)