diff --git a/runtime/install.sh b/runtime/install.sh
index d4d332e4e..279a2ba5a 100755
--- a/runtime/install.sh
+++ b/runtime/install.sh
@@ -12,6 +12,9 @@ if [ -f brillvm/rt.bc ]; then
 fi
 
 cd runtime
+# Duplicate runtime.bc files can mess things up,
+# so make sure we start from a clean slate.
+cargo clean
 cargo rustc --release -- --emit=llvm-bc 
 cp ./target/release/deps/runtime-*.bc ./rt.bc
 cc -c rt.c -o rt.o