diff --git a/compiler/sighashes.nim b/compiler/sighashes.nim
index d6db0b0fa0..7705ff62d9 100644
--- a/compiler/sighashes.nim
+++ b/compiler/sighashes.nim
@@ -190,9 +190,10 @@ proc hashType(c: var MD5Context, t: PType; flags: set[ConsiderFlag]; conf: Confi
     if CoConsiderOwned in flags:
       c &= char(t.kind)
     c.hashType t.skipModifier, flags, conf
-  of tyBool, tyChar, tyInt..tyUInt64:
-    # no canonicalization for integral types, so that e.g. ``pid_t`` is
-    # produced instead of ``NI``:
+  of tyBool, tyChar, tyPointer, tyCstring, tyInt..tyUInt64:
+    # no canonicalization for builtin scalar-ish / pointer-like types, so
+    # that e.g. ``pid_t`` or an imported ``pointer`` alias keep their
+    # backend spelling instead of collapsing into the generic Nim builtin:
     c &= char(t.kind)
     if t.sym != nil and {sfImportc, sfExportc} * t.sym.flags != {}:
       c.hashSym(t.sym)
@@ -533,4 +534,3 @@ proc idOrSig*(s: PSym, currentModule: string,
     if counter != 0:
       result.add "_" & rope(counter+1)
     sigCollisions.inc(sig)
-
diff --git a/tests/ccgbugs/tsighash_typename_regression.nim b/tests/ccgbugs/tsighash_typename_regression.nim
index b93eebd204..e9aa7df712 100644
--- a/tests/ccgbugs/tsighash_typename_regression.nim
+++ b/tests/ccgbugs/tsighash_typename_regression.nim
@@ -30,3 +30,13 @@ block:
 
   var x = M(x: 1)
   doAssert(x.x == 1)
+
+block: # bug #25931
+  type
+    N {.importc: "const void *".} = pointer
+    S = object
+        f: proc (_: N) {.cdecl.}
+    #var _: proc (_: pointer) {.cdecl.}
+  proc d(_: proc (_: pointer) {.cdecl.}) = discard
+  discard S()
+  d(proc (_: pointer) {.cdecl.} = discard)