diff --git a/Project.toml b/Project.toml
index 22589770..884898d3 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "Mooncake"
 uuid = "da2b9cff-9c12-43a0-ae48-6db2b0edb7d6"
 authors = ["Will Tebbutt, Hong Ge, and contributors"]
-version = "0.4.21"
+version = "0.4.22"
 
 [deps]
 ADTypes = "47edcb42-4c32-4615-8424-f2b9edc5f35b"
diff --git a/src/interpreter/s2s_reverse_mode_ad.jl b/src/interpreter/s2s_reverse_mode_ad.jl
index ebc7592a..67ef69a4 100644
--- a/src/interpreter/s2s_reverse_mode_ad.jl
+++ b/src/interpreter/s2s_reverse_mode_ad.jl
@@ -1195,7 +1195,7 @@ function pullback_ir(
         rvs_block = BBlock(blk_id, vcat(comms_insts, rvs_ad_stmts, additional_stmts))
         return vcat(rvs_block, new_blocks)
     end
-    main_blocks = vcat(main_blocks...)
+    main_blocks = reduce(vcat, main_blocks)
 
     # Create an exit block. Dereferences reverse-data for arguments, increments a zero rdata
     # against it to ensure that it is of the correct type, and returns it.