3 files changed, 9 insertions, 0 deletions
diff --git a/tvix/eval/src/compiler/mod.rs b/tvix/eval/src/compiler/mod.rs
index 160433904dc7..793f0566e9de 100644
--- a/tvix/eval/src/compiler/mod.rs
+++ b/tvix/eval/src/compiler/mod.rs
@@ -471,6 +471,7 @@ impl Compiler<'_> {
     fn compile_assert(&mut self, slot: LocalIdx, node: ast::Assert) {
         // Compile the assertion condition to leave its value on the stack.
         self.compile(slot, node.condition().unwrap());
+        self.emit_force(&node.condition().unwrap());
         self.push_op(OpCode::OpAssert, &node.condition().unwrap());
 
         // The runtime will abort evaluation at this point if the
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-assert-thunk-condition.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-assert-thunk-condition.exp
new file mode 100644
index 000000000000..aabe6ec3909c
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-assert-thunk-condition.exp
@@ -0,0 +1 @@
+21
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-assert-thunk-condition.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-assert-thunk-condition.nix
new file mode 100644
index 000000000000..8934b3d8cf02
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-assert-thunk-condition.nix
@@ -0,0 +1,7 @@
+let
+  condition = x: y: x < y;
+in
+
+# The function application here will become a thunk which verifies that
+# assert forces the condition expression correctly.
+assert condition 21 42; 21