diff --git a/Cargo.toml b/Cargo.toml
index 37f8fe30..c713ac86 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -75,8 +75,14 @@ unsafe_code = "forbid"
 dbg_macro = "warn"
 todo = "warn"
 
+# `"*"` matches every non-workspace package: crates.io dependencies and the
+# vendored crates under `vendor/` (excluded from the workspace). Our own crates
+# keep full debug info. Dependencies keep only line tables, so backtraces still
+# show file and line, but debug info for the whole dependency graph stays out of
+# every test binary (each UI test binary had a 500-600 MB PDB on Windows, #454).
 [profile.dev.package."*"]
 opt-level = 2
+debug = "line-tables-only"
 
 [profile.dev]
 opt-level = 1