diff --git a/crates/punktfunk-host/src/inject/proto/steam_proto.rs b/crates/punktfunk-host/src/inject/proto/steam_proto.rs
index fdcb0ef1..d67e92bb 100644
--- a/crates/punktfunk-host/src/inject/proto/steam_proto.rs
+++ b/crates/punktfunk-host/src/inject/proto/steam_proto.rs
@@ -542,12 +542,16 @@ pub fn deck_unit_id(index: u8) -> u32 {
     0x5046_0000 | index as u32
 }
 
-/// A Steam-accepted alphanumeric unit serial (a real Deck's is e.g. `"FVZZ4200469B"`; Steam rejects
-/// a too-short/oddly-formatted one as "Invalid or missing unit serial number" and substitutes its
-/// own — benign, but we present a clean 12-char one). Derived from [`deck_unit_id`] so the `0xAE`
-/// serial reply and the `0x83` unit-id attrs stay consistent.
+/// A Steam-accepted alphanumeric unit serial (a real Deck's is e.g. `"FVZZ4200469B"`). Steam
+/// validates the serial's FORMAT before accepting it: a `"PF"`-leading serial is REJECTED
+/// ("Invalid or missing unit serial number …") and Steam then substitutes a hash AND mangles the
+/// displayed controller name (observed as "Steam Deck Controllerggg" on Windows). An `'F'`-leading
+/// serial passes, so we keep the PunktFunk marker one slot in (`"FVPF"`) — still distinct from a
+/// real Deck's `"FVZZ"` for the self-detection below while satisfying Steam's format check.
+/// Derived from [`deck_unit_id`] so the `0xAE` serial reply and the `0x83` unit-id attrs stay
+/// consistent. (The Windows UMDF driver mirrors this exact format — see pf-dualsense lib.rs.)
 pub fn deck_serial(index: u8) -> String {
-    format!("PFDK{:08X}", deck_unit_id(index))
+    format!("FVPF{:08X}", deck_unit_id(index))
 }
 
 /// The neutral 64-byte Deck input report (header only, all controls released) — the report the
@@ -914,7 +918,7 @@ mod tests {
     fn deck_feature_reply_contract() {
         let serial = deck_serial(0);
         let unit_id = deck_unit_id(0);
-        assert_eq!(serial, "PFDK50460000"); // 12-char alphanumeric, derived from the unit id
+        assert_eq!(serial, "FVPF50460000"); // 12-char alphanumeric, derived from the unit id
         assert_eq!(serial.len(), 12);
 
         // 0x83 GET_ATTRIBUTES_VALUES: header + (0x0a, unit_id) at the 3rd attribute slot.
diff --git a/crates/punktfunk-host/src/punktfunk1.rs b/crates/punktfunk-host/src/punktfunk1.rs
index b9450d0c..5052e978 100644
--- a/crates/punktfunk-host/src/punktfunk1.rs
+++ b/crates/punktfunk-host/src/punktfunk1.rs
@@ -2865,7 +2865,7 @@ fn degrade_if_no_uhid(chosen: GamepadPref) -> GamepadPref {
 /// device (vhci resolves through `vhci_hcd`, NOT `/devices/virtual/`), so a just-ended session's
 /// pad still detaching — or a concurrent session's live one — read as "physical" and degraded
 /// every back-to-back Deck session to DualSense (observed live on Bazzite 2026-07-04). Ours are
-/// recognizable by the `PFDK…` serial ([`steam_proto::deck_serial`]) in `HID_UNIQ`, with the
+/// recognizable by the `FVPF…` serial ([`steam_proto::deck_serial`]) in `HID_UNIQ`, with the
 /// vhci path as belt and braces.
 #[cfg(target_os = "linux")]
 fn physical_steam_controller_present() -> bool {
@@ -2877,7 +2877,7 @@ fn physical_steam_controller_present() -> bool {
             return false;
         }
         if std::fs::read_to_string(e.path().join("uevent"))
-            .is_ok_and(|u| u.lines().any(|l| l.starts_with("HID_UNIQ=PFDK")))
+            .is_ok_and(|u| u.lines().any(|l| l.starts_with("HID_UNIQ=FVPF")))
         {
             return false; // one of our own virtual Decks
         }
diff --git a/packaging/windows/drivers/pf-dualsense/src/lib.rs b/packaging/windows/drivers/pf-dualsense/src/lib.rs
index 804611f8..2f61d549 100644
--- a/packaging/windows/drivers/pf-dualsense/src/lib.rs
+++ b/packaging/windows/drivers/pf-dualsense/src/lib.rs
@@ -673,21 +673,31 @@ fn deck_feature_reply() -> [u8; 64] {
         .unwrap_or(0)
         & 0xFF;
     let unit_id: u32 = 0x5046_0000 | idx;
-    let serial = format!("PFDK{unit_id:08X}");
-    let serial = serial.as_bytes();
+    // Steam validates the unit serial's PREFIX before accepting it: a "PF"-leading serial is
+    // REJECTED ("Invalid or missing unit serial number …") and Steam then substitutes a hash and
+    // MANGLES the displayed name ("Steam Deck Controllerggg"). An 'F'-leading serial passes, so we
+    // keep our PunktFunk marker one slot in ("FVPF") — still distinct enough for the Linux side's
+    // physical-Deck self-detection while satisfying Steam's format check. (This, not the build-time
+    // attributes below, is what un-mangles the name — verified by A/B on .173.)
+    let unit_serial = format!("FVPF{unit_id:08X}");
+    let unit_serial = unit_serial.as_bytes();
     let mut r = [0u8; 64];
     match last[0] {
         0x83 => {
             // GET_ATTRIBUTES_VALUES: [0x83, 0x2d, then 9x (attr-id, value u32-LE)].
             r[0] = 0x83;
             r[1] = 0x2D;
+            // Attribute semantics per SDL's controller_constants.h: 0x04 = FIRMWARE_BUILD_TIME
+            // and 0x0A = BOOTLOADER_BUILD_TIME are unix timestamps that must look like real build
+            // dates (the old unit-id-derived junk here was cosmetic; the name mangling was the
+            // serial prefix). Uniqueness rides the serial.
             let attrs: [(u8, u32); 9] = [
-                (0x01, 0x1205),
-                (0x02, 0),
-                (0x0A, unit_id),
-                (0x04, unit_id ^ 0x5555_5555),
-                (0x09, 0x2E),
-                (0x0B, 0x0FA0),
+                (0x01, 0x1205),      // ATTRIB_PRODUCT_ID
+                (0x02, 0),           // ATTRIB_CAPABILITIES
+                (0x0A, 0x6408_9000), // ATTRIB_BOOTLOADER_BUILD_TIME (2023-03-08)
+                (0x04, 0x66A8_C000), // ATTRIB_FIRMWARE_BUILD_TIME (2024-07-30)
+                (0x09, 0x2E),        // ATTRIB_BOARD_REVISION (captured)
+                (0x0B, 0x0FA0),      // ATTRIB_CONNECTION_INTERVAL_IN_US (4 ms)
                 (0x0D, 0),
                 (0x0C, 0),
                 (0x0E, 0),
@@ -700,12 +710,19 @@ fn deck_feature_reply() -> [u8; 64] {
             }
         }
         0xAE => {
-            // GET_STRING_ATTRIBUTE: [0xAE, len, attr, ascii…].
-            let attr = if last[2] != 0 { last[2] } else { 0x01 };
+            // GET_STRING_ATTRIBUTE: [0xAE, len, attr, ascii…]. Steam requests two strings: attr
+            // 0x00 = ATTRIB_STR_BOARD_SERIAL (the PCB serial) and 0x01 = ATTRIB_STR_UNIT_SERIAL.
+            // Echo the exact attr requested (last[2]) — the unit serial is the one that matters:
+            // getting its format right (FVPF…, see above) is what un-mangles the displayed name.
+            // Steam ALSO validates the PCB serial against a Valve-internal format we don't have a
+            // real capture of; it logs "Deck Controller PCB Serial# invalid" for ANY value we send
+            // (including an empty one — verified on .173), but that line is BENIGN: unlike a bad
+            // unit serial, it does not mangle the name, change the handle, or block promotion. So we
+            // serve the unit serial for both attrs and accept the log.
             r[0] = 0xAE;
-            r[1] = serial.len() as u8;
-            r[2] = attr;
-            r[3..3 + serial.len()].copy_from_slice(serial);
+            r[1] = unit_serial.len() as u8;
+            r[2] = last[2];
+            r[3..3 + unit_serial.len()].copy_from_slice(unit_serial);
         }
         _ => r.copy_from_slice(&last),
     }
@@ -779,7 +796,7 @@ fn on_get_string(request: &Request) -> NTSTATUS {
                     .map(|v| v.read_u32(OFF_PAD_INDEX))
                     .unwrap_or(0)
                     & 0xFF;
-                format!("PFDK{:08X}", 0x5046_0000u32 | idx)
+                format!("FVPF{:08X}", 0x5046_0000u32 | idx)
             }
             _ => "35533AD6E774".into(),
         },