diff --git a/Project.toml b/Project.toml
index 44eab571f..ae7ab52de 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "SciMLBase"
 uuid = "0bca4576-84f4-4d90-8ffe-ffa030f20462"
 authors = ["Chris Rackauckas <accounts@chrisrackauckas.com> and contributors"]
-version = "1.92.5"
+version = "1.92.6"
 
 [deps]
 ADTypes = "47edcb42-4c32-4615-8424-f2b9edc5f35b"
diff --git a/src/utils.jl b/src/utils.jl
index d013c9ac9..b2c8a57a9 100644
--- a/src/utils.jl
+++ b/src/utils.jl
@@ -205,6 +205,19 @@ struct FunctionArgumentsError <: Exception
     f::Any
 end
 
+function sig_has_vararg(sig)
+    isvarargtype(x) = x isa typeof(Vararg)
+    # unwrap unionalls
+    while sig isa UnionAll
+        sig = sig.body
+    end
+    if sig <: Tuple
+        return any(isvarargtype, sig.parameters)
+    else
+        error("SciMLBase is messing around with types that it doesn't understand. Please file an issue")
+    end
+end
+
 function Base.showerror(io::IO, e::FunctionArgumentsError)
     println(io, ARGUMENTS_ERROR_MESSAGE)
     print(io, "Offending function: ")
@@ -255,8 +268,7 @@ function isinplace(f, inplace_param_number, fname = "f", iip_preferred = true;
             # Find if there's a `f(args...)` dispatch
             # If so, no error
             for i in 1:length(nargs)
-                if nargs[i] < inplace_param_number &&
-                   any(isequal(Vararg{Any}), methods(f).ms[1].sig.parameters)
+                if nargs[i] < inplace_param_number && sig_has_vararg(methods(f).ms[1].sig)
                     # If varargs, assume iip
                     return iip_preferred
                 end
@@ -274,8 +286,7 @@ function isinplace(f, inplace_param_number, fname = "f", iip_preferred = true;
         # Find if there's a `f(args...)` dispatch
         # If so, no error
         for i in 1:length(nargs)
-            if nargs[i] < inplace_param_number &&
-               any(isequal(Vararg{Any}), methods(f).ms[1].sig.parameters)
+            if nargs[i] < inplace_param_number && sig_has_vararg(methods(f).ms[1].sig)
                 # If varargs, assume iip
                 return iip_preferred
             end
diff --git a/test/function_building_error_messages.jl b/test/function_building_error_messages.jl
index bb5414344..0544c37b0 100644
--- a/test/function_building_error_messages.jl
+++ b/test/function_building_error_messages.jl
@@ -463,3 +463,13 @@ optf(u) = 1.0
 optf(u, p) = 1.0
 OptimizationFunction(optf)
 OptimizationProblem(optf, 1.0)
+
+# Varargs
+var1(u...) = 1.0
+var2(u::Vararg{Any, N}) where N = 1.0
+var3(u::Vararg{Int, N}) where N = 1.0
+var4(u::Vararg{Vector{T}, N}) where {T, N} = 1.0
+OptimizationFunction(var1)
+OptimizationFunction(var2)
+OptimizationFunction(var3)
+OptimizationFunction(var4)