diff --git a/artiq/test/lit/monomorphism/bug_1252.py b/artiq/test/lit/monomorphism/bug_1252.py
new file mode 100644
index 000000000..e00a899ab
--- /dev/null
+++ b/artiq/test/lit/monomorphism/bug_1252.py
@@ -0,0 +1,8 @@
+# RUN: %python -m artiq.compiler.testbench.irgen %s >%t
+# RUN: OutputCheck %s --file-to-check=%t
+
+# CHECK-L: %BLT.round = numpy.int64 builtin(round) float
+def frequency_to_ftw(frequency):
+    return int64(round(1e-9*frequency))
+
+frequency_to_ftw(1e9)