diff --git a/test/test_testserver_precompile.jl b/test/test_testserver_precompile.jl
new file mode 100644
index 0000000..9bd350d
--- /dev/null
+++ b/test/test_testserver_precompile.jl
@@ -0,0 +1,42 @@
+@testitem "The test process environment precompiles cleanly" begin
+    # `TestItemServer` assembles the vendored packages by hand, and an override that
+    # *redefines* one of their methods rather than adding a more specific one is a method
+    # overwrite — which Julia rejects outright while a package precompiles.
+    #
+    # Nothing else in this suite notices directly: precompilation is warn-only on the path a
+    # test process takes, so the package still loads. What it costs is a full source reload
+    # of the vendored stack in every test process (tens of seconds each) and a precompile
+    # banner on its stderr, which then lands in whatever a test item captures. Those
+    # second-order effects are how it last surfaced, in assertions about process output.
+    # Assert the cache is actually built instead.
+    env_dir = normpath(joinpath(@__DIR__, "..", "testprocess", "environments"))
+    versioned = joinpath(env_dir, "v$(VERSION.major).$(VERSION.minor)")
+    project = isdir(versioned) ? versioned : joinpath(env_dir, "fallback")
+
+    # `Base.compilecache` rather than `Pkg.precompile`: it rebuilds unconditionally, so a
+    # cache some other test item already wrote cannot short-circuit the check, and it reports
+    # a failure as a `Core.PrecompilableError` return value — `Pkg.precompile` reports one as
+    # a `?` in its progress list and still exits 0.
+    code = """
+        result = Base.compilecache(Base.identify_package("TestItemServer"))
+        result isa Tuple || exit(1)
+        """
+    julia = joinpath(Sys.BINDIR, Base.julia_exename())
+    cmd = `$julia --startup-file=no --history-file=no --project=$project -e $code`
+
+    io = IOBuffer()
+    process = run(pipeline(ignorestatus(cmd), stdout=io, stderr=io))
+    output = String(take!(io))
+
+    ok = success(process) &&
+        !occursin("Method overwriting is not permitted", output) &&
+        !occursin("overwritten at", output)
+    if !ok
+        println("── precompiling TestItemServer in $project ──")
+        println(output)
+    end
+
+    @test success(process)
+    @test !occursin("Method overwriting is not permitted", output)
+    @test !occursin("overwritten at", output)
+end
diff --git a/testprocess/TestItemServer/src/pkg_imports.jl b/testprocess/TestItemServer/src/pkg_imports.jl
index d6f39be..3cd473d 100644
--- a/testprocess/TestItemServer/src/pkg_imports.jl
+++ b/testprocess/TestItemServer/src/pkg_imports.jl
@@ -90,6 +90,24 @@ module Revise
         using ...LoweredCodeUtils: next_or_nothing!, callee_matches
 
         include("../../../packages/Revise/src/packagedef.jl")
+
+        # Revise seeds the cache source hash with a `UInt64`, while the seed `hash` takes is a
+        # `UInt` — 32 bits wide on a 32 bit platform. Its package callback dies there with
+        # `MethodError: no method matching hash(::UInt64, ::UInt64)`, and every test item that
+        # loads a package in that process reports the failed callback as its own error.
+        #
+        # `packages/` holds git subtrees that are never edited by hand, so the method is added
+        # here instead, where this module is assembled. It is deliberately *more specific* than
+        # the vendored `cache_src_id(inc)` rather than a redefinition of it: redefining is
+        # method overwriting, which Julia rejects outright while this package precompiles. Both
+        # call sites pass a `Base.CacheHeaderIncludes`, so this one wins dispatch. `inc.hash` is
+        # a `UInt32`, so widening it to `UInt` is exact. Guarded like the definition it shadows
+        # (https://github.com/JuliaLang/julia/pull/49866); older versions hash `inc.mtime` and
+        # are unaffected. Drop this once the fix is in a released Revise.
+        @static if Sys.WORD_SIZE == 32 && VERSION >= v"1.11.0-DEV.683" &&
+                   isdefined(Base, :CacheHeaderIncludes)
+            cache_src_id(inc::Base.CacheHeaderIncludes) = hash(inc.fsize, UInt(inc.hash))
+        end
     elseif VERSION >= v"1.6.0"
         using ..OrderedCollections
         using ..LoweredCodeUtils