diff --git a/bosk-core/src/main/java/io/vena/bosk/Bosk.java b/bosk-core/src/main/java/io/vena/bosk/Bosk.java
index 60f37de9..d6db44b3 100644
--- a/bosk-core/src/main/java/io/vena/bosk/Bosk.java
+++ b/bosk-core/src/main/java/io/vena/bosk/Bosk.java
@@ -650,7 +650,11 @@ public final class ReadContext implements AutoCloseable {
 		private ReadContext() {
 			originalRoot = rootSnapshot.get();
 			if (originalRoot == null) {
-				snapshot = currentRoot;
+				try {
+					snapshot = requireNonNull(currentRoot);
+				} catch (NullPointerException e) {
+					throw new IllegalStateException("Bosk constructor has not yet finished; cannot create a ReadContext", e);
+				}
 				rootSnapshot.set(snapshot);
 				LOGGER.trace("New {}", this);
 			} else {
diff --git a/bosk-core/src/test/java/io/vena/bosk/BoskConstructorTest.java b/bosk-core/src/test/java/io/vena/bosk/BoskConstructorTest.java
index 675494e9..db1e7ce1 100644
--- a/bosk-core/src/test/java/io/vena/bosk/BoskConstructorTest.java
+++ b/bosk-core/src/test/java/io/vena/bosk/BoskConstructorTest.java
@@ -128,6 +128,16 @@ void defaultRoot_matches() {
 		}
 	}
 
+	@Test
+	void readContextDuringDriverFactory_throws() {
+		assertThrows(IllegalStateException.class, ()->{
+			new Bosk<>("readContext", SimpleTypes.class, newEntity(), (b,d) -> {
+				try (val __ = b.readContext()) {}
+				return d;
+			});
+		});
+	}
+
 	////////////////
 	//
 	//  Helpers