diff --git a/crates/hip-bridge/map.md b/crates/hip-bridge/map.md
index 7b800c929..b2d455456 100644
--- a/crates/hip-bridge/map.md
+++ b/crates/hip-bridge/map.md
@@ -23,21 +23,21 @@ _Generated by `scripts/check-crate-maps.py` from the tree — do not edit inside
 
 | File | Lines | Public items | Tests |
 |---|---:|---:|---:|
-| [`src/error.rs`](src/error.rs) | 70 | 8 | 0 |
-| [`src/ffi.rs`](src/ffi.rs) | 1,772 | 96 | 0 |
+| [`src/error.rs`](src/error.rs) | 132 | 10 | 2 |
+| [`src/ffi.rs`](src/ffi.rs) | 1,799 | 98 | 0 |
 | [`src/kernarg.rs`](src/kernarg.rs) | 178 | 14 | 3 |
-| [`src/lib.rs`](src/lib.rs) | 181 | 18 | 2 |
-| [`src/rccl.rs`](src/rccl.rs) | 470 | 18 | 0 |
+| [`src/lib.rs`](src/lib.rs) | 222 | 19 | 2 |
+| [`src/rccl.rs`](src/rccl.rs) | 475 | 18 | 0 |
 | [`src/rocblas.rs`](src/rocblas.rs) | 744 | 17 | 3 |
 | [`src/rocsolver.rs`](src/rocsolver.rs) | 374 | 12 | 3 |
-| [`src/vmm.rs`](src/vmm.rs) | 566 | 12 | 4 |
+| [`src/vmm.rs`](src/vmm.rs) | 567 | 12 | 4 |
 
 ### Public API surface
 
-- [`src/error.rs`](src/error.rs): `HipErrorCode`, `HipResult`, `HIP_ERROR_INVALID_IMAGE`, `HIP_ERROR_PEER_ACCESS_UNSUPPORTED`, `HIP_ERROR_PEER_ACCESS_ALREADY_ENABLED`, `HIP_ERROR_PEER_ACCESS_NOT_ENABLED`, `HipError`, `new`
-- [`src/ffi.rs`](src/ffi.rs): `launch_counters`, `record`, `record_bytes`, `time_ns`, `count`, `bytes`, `reset`, `HipMemGenericAllocationHandle`, `HIP_MEM_LOCATION_TYPE_DEVICE`, `HIP_MEM_ALLOCATION_TYPE_PINNED`, `HIP_MEM_ACCESS_FLAGS_PROT_READ_WRITE`, `HIP_MEM_ALLOCATION_GRANULARITY_MINIMUM`, +84 more
+- [`src/error.rs`](src/error.rs): `HipErrorCode`, `HipResult`, `HIP_ERROR_INVALID_IMAGE`, `HIP_ERROR_PEER_ACCESS_UNSUPPORTED`, `HIP_ERROR_PEER_ACCESS_ALREADY_ENABLED`, `HIP_ERROR_PEER_ACCESS_NOT_ENABLED`, `LaunchContext`, `HipError`, `new`, `with_kernel`
+- [`src/ffi.rs`](src/ffi.rs): `launch_counters`, `record`, `record_bytes`, `time_ns`, `count`, `bytes`, `reset`, `HipMemGenericAllocationHandle`, `HIP_ERROR_NOT_READY`, `HIP_MEM_LOCATION_TYPE_DEVICE`, `HIP_MEM_ALLOCATION_TYPE_PINNED`, `HIP_MEM_ACCESS_FLAGS_PROT_READ_WRITE`, +86 more
 - [`src/kernarg.rs`](src/kernarg.rs): `KernargBlob`, `new`, `with_capacity`, `len`, `is_empty`, `push_ptr`, `push_u32`, `push_i32`, `push_f32`, `push_u64`, `pad_to`, `as_mut_slice`, +2 more
-- [`src/lib.rs`](src/lib.rs): `error`, `ffi`, `kernarg`, `rccl`, `rocblas`, `rocsolver`, `vmm`, `MemcpyKind`, `MemoryType`, `from_raw`, `DeviceBuffer`, `as_ptr`, +6 more
+- [`src/lib.rs`](src/lib.rs): `error`, `ffi`, `kernarg`, `rccl`, `rocblas`, `rocsolver`, `vmm`, `MemcpyKind`, `MemoryType`, `from_raw`, `DeviceBuffer`, `as_ptr`, +7 more
 - [`src/rccl.rs`](src/rccl.rs): `NCCL_SUCCESS`, `RcclError`, `RcclResult`, `RcclDataType`, `RcclRedOp`, `RcclComms`, `init_all`, `len`, `is_empty`, `version`, `group_start`, `group_end`, +6 more
 - [`src/rocblas.rs`](src/rocblas.rs): `RocblasError`, `RocblasResult`, `ROCBLAS_STATUS_SUCCESS`, `ROCBLAS_STATUS_INVALID_VALUE`, `RocblasOperation`, `RocblasDatatype`, `RocblasGemmAlgo`, `Rocblas`, `load`, `set_stream`, `handle`, `has_dgemm`, +5 more
 - [`src/rocsolver.rs`](src/rocsolver.rs): `ROCSOLVER_STATUS_SUCCESS`, `RocblasFill`, `RocblasDiagonal`, `RocsolverError`, `RocsolverResult`, `Rocsolver`, `load`, `load_from_handle`, `has_dpotri`, `dpotrf`, `dtrtri`, `dpotri`
@@ -56,6 +56,6 @@ _Generated by `scripts/check-crate-maps.py` from the tree — do not edit inside
 
 ### Totals
 
-- 8 modules · 4,355 lines · 195 public items · 15 tests · 8 examples
+- 8 modules · 4,491 lines · 200 public items · 17 tests · 8 examples
 
 <!-- crate-map:generated:end -->
diff --git a/crates/hip-bridge/src/rccl.rs b/crates/hip-bridge/src/rccl.rs
index 33786eb60..d83a0bb8b 100644
--- a/crates/hip-bridge/src/rccl.rs
+++ b/crates/hip-bridge/src/rccl.rs
@@ -101,13 +101,18 @@ impl RcclComms {
     /// `ncclCommInitAll`. Each comm[i] binds to `device_ids[i]`.
     pub fn init_all(device_ids: &[i32]) -> RcclResult<Self> {
         let lib = unsafe {
-            // Resolved ROCm roots first, bare sonames last, so RCCL is found on
-            // side-by-side and /opt/rocm/core-<ver> installs too.
-            let candidates = hipfire_config::rocm::library_candidates(&[
-                "librccl.so",
-                "librccl.so.1",
-                "librccl.so.1.0",
-            ]);
+            // `HIPFIRE_RCCL_LIB` first, then the resolved ROCm root.
+            // `library_candidates` stops at the selected root on purpose (an
+            // explicit root is authoritative; see `hipfire_config::rocm`), and
+            // RCCL follows that policy. The override is for distributions whose
+            // ROCm prefix does not carry RCCL: nixpkgs ships librccl in its own
+            // store path next to `rocmtoolkit-merged`.
+            const SONAMES: [&str; 3] = ["librccl.so", "librccl.so.1", "librccl.so.1.0"];
+            let mut candidates = Vec::new();
+            if let Ok(explicit) = hipfire_config::developer_var("HIPFIRE_RCCL_LIB") {
+                candidates.push(explicit);
+            }
+            candidates.extend(hipfire_config::rocm::library_candidates(&SONAMES));
             let mut loaded = None;
             for name in &candidates {
                 if let Ok(l) = Library::new(name) {
@@ -118,7 +123,7 @@ impl RcclComms {
             loaded.ok_or_else(|| RcclError {
                 status: 0,
                 context: format!(
-                    "failed to dlopen librccl.so. Tried: {:?}. Is RCCL installed (apt install rccl, or /opt/rocm/lib/librccl.so.1)?",
+                    "failed to dlopen librccl.so. Tried: {:?}. Is RCCL installed (apt install rccl, or /opt/rocm/lib/librccl.so.1)? If it lives outside the ROCm root, set HIPFIRE_RCCL_LIB=/path/to/librccl.so.",
                     candidates
                 ),
             })?
diff --git a/docs/env-vars.md b/docs/env-vars.md
index 766ebfc79..6b5a5d073 100644
--- a/docs/env-vars.md
+++ b/docs/env-vars.md
@@ -169,6 +169,7 @@ diagnostic and developer harness exports pending their cleanup.
 | `HIPFIRE_MAX_REQUEST_BYTES` | Body cap |
 | `HIPFIRE_SERVE_MAX_QUEUE` / `HIPFIRE_SERVE_QUEUE_TIMEOUT_MS` | Admission queue |
 | `HIPFIRE_EXPERIMENTAL_BUDGET_ALERT` | Research budget nudge |
+| `HIPFIRE_RCCL_LIB` | Explicit `librccl.so` path, tried before the ROCm root. For distributions whose ROCm prefix does not carry RCCL (nixpkgs: `rocmtoolkit-merged` has HIP/HSA, `librccl` is a separate store path). |
 | `HIPFIRE_DEVICES` / `HIPFIRE_TP` / `HIPFIRE_TP_USE_RCCL` | Multi-GPU / TP. `HIPFIRE_DEVICES` is the compatibility alias for `hardware.devices`; startup lowers its physical list to ROCr selectors plus matching HIP logical selectors. |
 | `HIPFIRE_ALLOW_MIXED_ARCH=1` | Mixed arch pairs |
 | `HIPFIRE_PP_LAYERS` / `HIPFIRE_PP_PFLASH` | Pipeline parallel |
@@ -286,7 +287,7 @@ Copyable user, developer, and retained-PM4 TOML profiles are in
 **Do not hand-edit rows below** except by re-running the source scan.
 **Generation method:** token scan over visible `*.rs`, `*.py`, and `*.sh`, excluding ignored/generated files.
 **Columns:** variable; up to two lexical source paths.
-**Count:** 715
+**Count:** 735
 
 | Variable | Example source path(s) |
 |---|---|
@@ -895,6 +896,7 @@ Copyable user, developer, and retained-PM4 TOML profiles are in
 | `HIPFIRE_QWEN_MOE_FINAL_NORM_RAW` | scripts/test_pr228_spiral_check.sh |
 | `HIPFIRE_QWEN_MTP` | crates/hipfire-daemon/src/main.rs, scripts/serve_harness.py |
 | `HIPFIRE_QWEN_PROMPT_CACHE` | crates/hipfire-daemon/src/main.rs |
+| `HIPFIRE_RCCL_LIB` | crates/hip-bridge/src/rccl.rs |
 | `HIPFIRE_RDNA2_VARIANT` | crates/hipfire-cli/src/main.rs, crates/rdna-compute/src/feature_flags.rs |
 | `HIPFIRE_RDNA3_HFQ4_LM_HEAD_K2048` | crates/rdna-compute/src/feature_flags.rs |
 | `HIPFIRE_RDNA3_HFQ4_MOE_GATE_UP_K2048` | crates/rdna-compute/src/feature_flags.rs |