diff --git a/meta/classes-recipe/rust-common.bbclass b/meta/classes-recipe/rust-common.bbclass
index 6bc42016d1..98b46c4e3c 100644
--- a/meta/classes-recipe/rust-common.bbclass
+++ b/meta/classes-recipe/rust-common.bbclass
@@ -114,6 +114,16 @@ RUST_HOST_SYS[vardepvalue] = "${RUST_HOST_SYS}"
 RUST_TARGET_SYS = "${@rust_base_triple(d, 'TARGET')}"
 RUST_TARGET_SYS[vardepvalue] = "${RUST_TARGET_SYS}"
 
+# Note: RUST_BUILD_SYS is intentionally NOT on BB_BASEHASH_IGNORE_VARS
+# (see meta/conf/bitbake.conf). rustc's crate SVH (Strict Version Hash)
+# is seeded by the stage0/stage1 bootstrap compiler whose fingerprint
+# depends on the BUILD host arch; that seed cascades through every
+# dependent crate's mangled symbols and rodata packing order. Excluding
+# RUST_BUILD_SYS from task hashes let a mixed-arch autobuilder pool
+# populate sstate on one worker arch and get a cache hit on a differently-
+# arched worker, producing byte-different (but semantically identical)
+# artifacts and failing reproducibility tests. See Yocto bug #15554.
+
 # wrappers to get around the fact that Rust needs a single
 # binary but Yocto's compiler and linker commands have
 # arguments. Technically the archiver is always one command but
diff --git a/meta/conf/bitbake.conf b/meta/conf/bitbake.conf
index bdf37d0da2..ee23459506 100644
--- a/meta/conf/bitbake.conf
+++ b/meta/conf/bitbake.conf
@@ -969,7 +969,7 @@ BB_HASHEXCLUDE_COMMON ?= "TMPDIR FILE PATH PWD BB_TASKHASH BBPATH BBSERVER DL_DI
     SSTATE_HASHEQUIV_OWNER CCACHE_TOP_DIR BB_HASHSERVE GIT_CEILING_DIRECTORIES \
     OMP_NUM_THREADS BB_CURRENTTASK"
 BB_BASEHASH_IGNORE_VARS ?= "${BB_HASHEXCLUDE_COMMON} PSEUDO_INCLUDE_PATHS BUILDHISTORY_DIR \
-    SSTATE_DIR SOURCE_DATE_EPOCH RUST_BUILD_SYS RUST_HOST_SYS RUST_TARGET_SYS"
+    SSTATE_DIR SOURCE_DATE_EPOCH RUST_HOST_SYS RUST_TARGET_SYS"
 BB_HASHCONFIG_IGNORE_VARS ?= "${BB_HASHEXCLUDE_COMMON} DATE TIME SSH_AGENT_PID \
     SSH_AUTH_SOCK PSEUDO_BUILD BB_ENV_PASSTHROUGH_ADDITIONS DISABLE_SANITY_CHECKS \
     PARALLEL_MAKE BB_NUMBER_THREADS BB_ORIGENV BB_INVALIDCONF BBINCLUDED \