diff --git a/compiler/sighashes.nim b/compiler/sighashes.nim
index 67607b31ed..fdb089d7f4 100644
--- a/compiler/sighashes.nim
+++ b/compiler/sighashes.nim
@@ -149,6 +149,17 @@ proc hashType(c: var MD5Context, t: PType; flags: set[ConsiderFlag]; conf: Confi
   # as properties are accessed and trigger lazy loading.
   backendEnsureMutable(t)
 
+  # Bare type-class keywords used as a typedesc without arguments (e.g. `array`,
+  # `range`, `distinct` passed to `signatureHash`) have no children, so the
+  # structural branches below would index a non-existent `elementType`. Hash them
+  # by kind (+ sym for an extra, stable distinction) — enough for a stable,
+  # distinct identity. (`seq`/`openArray`/`tuple` already fall through the empty
+  # `else` loop unharmed; this covers the branches that index `elementType`.)
+  if t.kind in {tyArray, tyRange, tyDistinct} and not t.hasElementType:
+    c &= char(t.kind)
+    if t.sym != nil: c.hashSym(t.sym)
+    return
+
   case t.kind
   of tyGenericInvocation:
     for a in t.kids:
diff --git a/compiler/vm.nim b/compiler/vm.nim
index a2baa5ec3c..851ba1d9db 100644
--- a/compiler/vm.nim
+++ b/compiler/vm.nim
@@ -1955,7 +1955,21 @@ proc rawExecute(c: PCtx, start: int, tos: PStackFrame): TFullReg =
       if regs[rb].node.kind != nkSym:
         stackTrace(c, tos, pc, "node is not a symbol")
       else:
-        regs[ra].node.strVal = $sigHash(regs[rb].node.sym, c.config)
+        let shSym = regs[rb].node.sym
+        # When `signatureHash` is applied to a type (e.g. a `T: typedesc`/generic
+        # param), hash the *type* it denotes, not the parameter symbol. Hashing the
+        # symbol routes through `hashNonProc`, which mixes in `s.disamb` — a
+        # per-module instantiation counter. Under incremental compilation the
+        # registering module and a consuming module instantiate the surrounding
+        # generic separately, get different `disamb`s, and produce different
+        # hashes for the same type (nim-serialization's auto-serialization lookup
+        # missed because of this). Hashing the underlying type via `hashType` is
+        # type-identity based and stable across the NIF boundary.
+        let shTyp = shSym.typ
+        if shTyp != nil and shTyp.kind == tyTypeDesc and shTyp.hasElementType:
+          regs[ra].node.strVal = $hashType(shTyp.elementType, c.config)
+        else:
+          regs[ra].node.strVal = $sigHash(shSym, c.config)
     of opcSlurp:
       decodeB(rkNode)
       createStr regs[ra]
diff --git a/koch.nim b/koch.nim
index e5909ea388..da43193469 100644
--- a/koch.nim
+++ b/koch.nim
@@ -617,7 +617,7 @@ proc runIcTestFile(inp: string) =
 # on a sibling helper (`timp` -> `myimp`, `tcompiletimeglobal` -> `mctglobal`),
 # which exercises the NIF import/load path the single-file tests do not.
 const icSuite = ["thallo", "tconverter", "timp", "tmiscs", "tparseutils",
-                 "tcompiletimeglobal"]
+                 "tcompiletimeglobal", "tsighashstable"]
 
 proc icTest(args: string) =
   temp("")
diff --git a/tests/ic/msighashstable.nim b/tests/ic/msighashstable.nim
new file mode 100644
index 0000000000..d5ce85d18a
--- /dev/null
+++ b/tests/ic/msighashstable.nim
@@ -0,0 +1,48 @@
+# Helper module for tsighashstable.nim (not a test itself; no `discard`).
+#
+# Models nim-serialization's auto-serialization registry: a flavor records which
+# types it auto-serializes in a `std/macrocache` keyed by `signatureHash(T)`,
+# computed through a generic `{.compileTime.}` func. The registration happens
+# here (at this module's compile time); the lookup happens in the importer.
+#
+# Under `nim ic` the two modules are compiled separately, so the generic
+# `getSig[T]` is instantiated independently on each side. `signatureHash` must
+# therefore hash the *type* `T` denotes, not the generic parameter symbol — the
+# latter mixes in a per-module `disamb` counter and diverges across the NIF
+# boundary, making the lookup miss.
+
+import std/[macrocache, macros, typetraits]
+
+type DefaultFlavor* = object
+
+macro calcSig*(T: typed): untyped =
+  doAssert(T.typeKind == ntyTypeDesc)
+  result = newLit(signatureHash(T))
+
+func getSig*(F: type DefaultFlavor, T: distinct type): string {.compileTime.} =
+  calcSig(T)
+
+func getTable*(F: type DefaultFlavor): CacheTable {.compileTime.} =
+  CacheTable("nsrzStableTable" & typetraits.name(F))
+
+func setAuto*(F: type DefaultFlavor, T: distinct type) {.compileTime.} =
+  let sig = F.getSig(T)
+  let table = F.getTable()
+  if not table.hasKey(sig):
+    table[sig] = newLit(1)
+
+func getAuto*(F: type DefaultFlavor, T: distinct type): bool {.compileTime.} =
+  let sig = F.getSig(T)
+  let table = F.getTable()
+  table.hasKey(sig)
+
+template autoCheck*(F: distinct type, T: distinct type, body) =
+  when not F.getAuto(T):
+    {.error: "auto serialization not enabled for `" & typetraits.name(T) & "`".}
+  else:
+    body
+
+static:
+  setAuto(DefaultFlavor, string)
+  setAuto(DefaultFlavor, SomeInteger)
+  setAuto(DefaultFlavor, seq)
diff --git a/tests/ic/tsighashstable.nim b/tests/ic/tsighashstable.nim
new file mode 100644
index 0000000000..11c20240d9
--- /dev/null
+++ b/tests/ic/tsighashstable.nim
@@ -0,0 +1,33 @@
+discard """
+output: '''ok string
+ok int
+ok seq'''
+"""
+
+# Regression test: `signatureHash(T)` must be stable across the NIF boundary so
+# that a macrocache keyed by it (nim-serialization's auto-serialization registry)
+# can be populated in one module and queried from another under `nim ic`.
+#
+# Before the fix, `signatureHash` hashed the generic *parameter symbol* (whose
+# `disamb` is a per-module instantiation counter) instead of the type it denotes.
+# The registering module (msighashstable) and this importer instantiated the
+# generic `getSig[T]` separately, got different `disamb`s, and the lookups for
+# `string`/`SomeInteger` missed -> `{.error: auto serialization not enabled.}`.
+
+import msighashstable
+
+proc writeStr(F: type DefaultFlavor, v: string) =
+  autoCheck(F, string):
+    echo "ok string"
+
+proc writeInt[T: SomeInteger](F: type DefaultFlavor, v: T) =
+  autoCheck(F, SomeInteger):
+    echo "ok int"
+
+proc writeSeq[T](F: type DefaultFlavor, v: seq[T]) =
+  autoCheck(F, seq):
+    echo "ok seq"
+
+writeStr(DefaultFlavor, "hi")
+writeInt(DefaultFlavor, 42)
+writeSeq(DefaultFlavor, @[1, 2, 3])