diff --git a/base/reflection.jl b/base/reflection.jl
index ee96b24dc6b96..706570303262c 100644
--- a/base/reflection.jl
+++ b/base/reflection.jl
@@ -1084,13 +1084,25 @@ function may_invoke_generator(method::Method, @nospecialize(atypes), sparams::Si
             end
         end
     end
-    for i = 1:length(at.parameters)
+    non_va_args = method.isva ? method.nargs - 1 : method.nargs
+    for i = 1:non_va_args
         if !isdispatchelem(at.parameters[i])
             if (ast_slotflag(code, 1 + i + nsparams) & SLOT_USED) != 0
                 return false
             end
         end
     end
+    if method.isva
+        # If the va argument is used, we need to ensure that all arguments that
+        # contribute to the va tuple are dispatchelemes
+        if (ast_slotflag(code, 1 + method.nargs + nsparams) & SLOT_USED) != 0
+            for i = (non_va_args+1):length(at.parameters)
+                if !isdispatchelem(at.parameters[i])
+                    return false
+                end
+            end
+        end
+    end
     return true
 end
 
diff --git a/test/staged.jl b/test/staged.jl
index 26e3dace1994b..4a953ffae33b8 100644
--- a/test/staged.jl
+++ b/test/staged.jl
@@ -304,3 +304,18 @@ end
     :(global x33243 = 2)
 end
 @test_throws ErrorException f33243()
+
+# https://github.com/JuliaDebug/CassetteOverlay.jl/issues/12
+# generated function with varargs and unfortunately placed unused slot
+@generated function f_vararg_generated(args...)
+    :($args)
+end
+g_vararg_generated() = f_vararg_generated((;), (;), Base.inferencebarrier((;)))
+let tup = g_vararg_generated()
+    @test !any(==(Any), tup)
+    # This is just to make sure that the test is actually testing what we want -
+    # the test only works if there's an unused that matches the position of the
+    # inferencebarrier argument above (N.B. the generator function itself
+    # shifts everything over by 1)
+    @test code_lowered(first(methods(f_vararg_generated)).generator.gen)[1].slotflags[5] == UInt8(0x00)
+end