diff --git a/Project.toml b/Project.toml
index f7f96cc..56d1036 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "MistyClosures"
 uuid = "dbe65cb8-6be2-42dd-bbc5-4196aaced4f4"
 authors = ["Will Tebbutt", "Frames White", "Hong Ge"]
-version = "1.0.3"
+version = "2.0.0"
 
 [compat]
 julia = "1.10"
diff --git a/src/MistyClosures.jl b/src/MistyClosures.jl
index 162e5eb..a7d338b 100644
--- a/src/MistyClosures.jl
+++ b/src/MistyClosures.jl
@@ -5,13 +5,18 @@ using Core.Compiler: IRCode
 
 import Base: show
 
+# As of 2.0, MistyClosure contains a reference to its IR. This is because `IRCode` is
+# a surprisingly bulky type (136B in 1.11.1 -- the same as 17 Float64s). Since especially
+# fast access to `ir` is never needed, it is fine to store it out-of-place, thus reducing
+# the size of a `MistyClosure` from 176B to 48B. This can have a substantial impact on the
+# performance of calling many `OpaqueClosure`s of the same type.
 struct MistyClosure{Toc<:OpaqueClosure}
     oc::Toc
-    ir::IRCode
+    ir::Base.RefValue{IRCode}
 end
 
 function MistyClosure(ir::IRCode, env...; kwargs...)
-    return MistyClosure(OpaqueClosure(ir, env...; kwargs...), ir)
+    return MistyClosure(OpaqueClosure(ir, env...; kwargs...), Ref(ir))
 end
 
 (mc::MistyClosure)(x::Vararg{Any, N}) where {N} = mc.oc(x...)
diff --git a/test/runtests.jl b/test/runtests.jl
index 304e0e1..19db474 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -16,7 +16,7 @@ end
     @test @inferred(mc(5.0)) == sin(5.0)
 
     # Default constructor.
-    mc_default = MistyClosure(OpaqueClosure(ir; do_compile=true), ir)
+    mc_default = MistyClosure(OpaqueClosure(ir; do_compile=true), Ref(ir))
     @test @inferred(mc_default(5.0) == sin(5.0))
 
     # Recommended constructor with env.
@@ -25,7 +25,7 @@ end
     @test @inferred(mc_with_env(4.0)) == Foo(5.0)(4.0)
 
     # Default constructor with env.
-    mc_env_default = MistyClosure(OpaqueClosure(ir_foo, 4.0; do_compile=true), ir_foo)
+    mc_env_default = MistyClosure(OpaqueClosure(ir_foo, 4.0; do_compile=true), Ref(ir_foo))
     @test @inferred(mc_env_default(5.0) == Foo(5.0)(4.0))
 
     # deepcopy