diff --git a/lib/www/server/lib/qc/index.js b/lib/www/server/lib/qc/index.js
index 7b444bf..038b773 100644
--- a/lib/www/server/lib/qc/index.js
+++ b/lib/www/server/lib/qc/index.js
@@ -10,6 +10,34 @@ const { projectHash, sequenceHash } = require('./last-modified');
 const { runShotsQC, saveShotsQC } = require('./shots');
 const { runSequenceQCs, saveSequenceQCs } = require('./sequences');
 
+/** Return true if the user has requested force running
+ * a QC that would normally not be scheduled to be run.
+ *
+ * This is done via the DOUGAL_FORCE_QC environment
+ * variable. The format is as follows:
+ *
+ * DOUGAL_FORCE_QC="project-id [sequence1 sequence2 … sequenceN]"
+ *
+ * A value of "project-id" re-runs QCs for all sequences of that
+ * project, whereas specifying sequences to be run affects only
+ * those sequences.
+ */
+function forceQC (projectId, sequenceNumber) {
+	if (process.env.DOUGAL_FORCE_QC) {
+		const [force_projectID, ...force_sequences ] = process.env.DOUGAL_FORCE_QC.split(/\s+/);
+		if (projectId == force_projectID) {
+			if (!sequenceNumber) {
+				return true;
+			} else if (!force_sequences.length) {
+				return true;
+			} else {
+				return force_sequences.map(i => Number(i)).some(i => i == sequenceNumber);
+			}
+		}
+	}
+	return false;
+}
+
 async function getProjectQCConfig (projectId) {
 	console.log("getProjectQCConfig");
 	const qcConfig = await configuration.get(projectId, "qc");
@@ -41,7 +69,7 @@ async function main () {
 			console.log("projectHash", projectHash);
 			console.log("lastQCHash", lastQCHash);
 
-			if (currentQCHash != lastQCHash) {
+			if (currentQCHash != lastQCHash || forceQC(projectId)) {
 				console.log("currentQCHash != lastQCHash", projectId, currentQCHash, lastQCHash);
 
 				// Fetch definitions and parameters
@@ -64,7 +92,7 @@ async function main () {
 						console.log("sequenceCurrentHash", sequenceCurrentHash);
 						console.log("sequenceLastQCHash", sequenceLastQCHash);
 
-						if (sequenceCurrentHash != sequenceLastQCHash) {
+						if (sequenceCurrentHash != sequenceLastQCHash || forceQC(projectId, sequenceNumber)) {
 
 							const results = await runShotsQC(projectId, sequenceNumber, shotQCs, parameters);