diff --git a/.github/workflows/bundle-ucm.yaml b/.github/workflows/bundle-ucm.yaml
index bd05781b39..e97da0292a 100644
--- a/.github/workflows/bundle-ucm.yaml
+++ b/.github/workflows/bundle-ucm.yaml
@@ -59,6 +59,7 @@ jobs:
                 --ghc-options='-O2' \
                 --local-bin-path ucm-bin \
                 --copy-bins \
+                --flag unison-runtime:optchecks \
                 && break;
           done
 
diff --git a/unison-runtime/package.yaml b/unison-runtime/package.yaml
index aa8a9713a1..8d874dfe1f 100644
--- a/unison-runtime/package.yaml
+++ b/unison-runtime/package.yaml
@@ -12,6 +12,13 @@ flags:
   stackchecks:
     manual: true
     default: false
+
+  # Run optimization assertion tests, make sure this runs with O2
+  optchecks:
+    manual: true
+    default: false
+
+  # Dumps core for debugging to unison-runtime/.stack-work/dist/<arch>/ghc-x.y.z/build/
   dumpcore:
     manual: true
     default: false
@@ -21,9 +28,9 @@ when:
     cpp-options: -DARRAY_CHECK
   - condition: flag(stackchecks)
     cpp-options: -DSTACK_CHECK
-    # Run optimization assertion tests, make sure this runs with O2
   - condition: flag(optchecks)
-    ghc-options: -O2 -DOPT_CHECK
+    ghc-options: -O2
+    cpp-options: -DOPT_CHECK
   - condition: flag(dumpcore)
     ghc-options: -ddump-simpl -ddump-stg-final -ddump-to-file -dsuppress-coercions -dsuppress-idinfo -dsuppress-module-prefixes -ddump-str-signatures -ddump-simpl-stats # -dsuppress-type-applications -dsuppress-type-signatures
 
diff --git a/unison-runtime/unison-runtime.cabal b/unison-runtime/unison-runtime.cabal
index f6b622cff3..b908088591 100644
--- a/unison-runtime/unison-runtime.cabal
+++ b/unison-runtime/unison-runtime.cabal
@@ -25,6 +25,10 @@ flag dumpcore
   manual: True
   default: False
 
+flag optchecks
+  manual: True
+  default: False
+
 flag stackchecks
   manual: True
   default: False
@@ -148,6 +152,9 @@ library
     cpp-options: -DARRAY_CHECK
   if flag(stackchecks)
     cpp-options: -DSTACK_CHECK
+  if flag(optchecks)
+    ghc-options: -O2
+    cpp-options: -DOPT_CHECK
   if flag(dumpcore)
     ghc-options: -ddump-simpl -ddump-stg-final -ddump-to-file -dsuppress-coercions -dsuppress-idinfo -dsuppress-module-prefixes -ddump-str-signatures -ddump-simpl-stats
 
@@ -232,5 +239,8 @@ test-suite runtime-tests
     cpp-options: -DARRAY_CHECK
   if flag(stackchecks)
     cpp-options: -DSTACK_CHECK
+  if flag(optchecks)
+    ghc-options: -O2
+    cpp-options: -DOPT_CHECK
   if flag(dumpcore)
     ghc-options: -ddump-simpl -ddump-stg-final -ddump-to-file -dsuppress-coercions -dsuppress-idinfo -dsuppress-module-prefixes -ddump-str-signatures -ddump-simpl-stats