diff --git a/ext/SciMLBaseRCallExt.jl b/ext/SciMLBaseRCallExt.jl
index bdcd596a4..38a61a7f2 100644
--- a/ext/SciMLBaseRCallExt.jl
+++ b/ext/SciMLBaseRCallExt.jl
@@ -3,8 +3,9 @@ module SciMLBaseRCallExt
 using RCall: RFunction
 using SciMLBase
 
-function SciMLBase.numargs(f::RFunction)
-    R"formals"(f)
+# Always assume a function from R is not in-place because copy-on-write disallows it!
+function SciMLBase.isinplace(f::RFunction, args...; kwargs...)
+    false
 end
 
-end
+end
\ No newline at end of file