diff --git a/src/lib/meson.build b/src/lib/meson.build
index 90a1c8ad..b0abdaa2 100644
--- a/src/lib/meson.build
+++ b/src/lib/meson.build
@@ -191,7 +191,17 @@ libxce = static_library('xce',
 # for consumers OUTSIDE the libxce target itself. link_with alone does not
 # propagate this: it only orders the LINK step after libxce is built, not
 # a consumer's own COMPILE steps against a header libxce never installs.
-libxce_dep = declare_dependency(link_with: libxce, sources: [gen_srcs],
+#
+# build-time dedup: this used to pass the WHOLE custom_target, which made
+# every consumer target compile controller.capnp.c itself -- 143 separate
+# compiles of a 9.5s/293MB-RSS/3.3MB-object TU (asan profile), ~35% of a
+# full clean build's serial work and ~470MB of duplicate .o files on disk.
+# Indexing to gen_srcs[1] (the .h output only) keeps everything bug-1798
+# needed: a custom_target output still carries the dependency edge on the
+# whole codegen step (custom_target always builds ALL of its outputs
+# atomically), and a .h source is never compiled. The .c output is compiled
+# exactly once, inside libxce above, and every consumer links the archive.
+libxce_dep = declare_dependency(link_with: libxce, sources: [gen_srcs[1]],
                                 dependencies: libxce_deps)
 # libxce_shared_dep = declare_dependency(link_with: libxce_shared)