diff --git a/Cargo.toml b/Cargo.toml
index 2f688c3067..c27c412a16 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -229,6 +229,34 @@ codegen-units = 16
 strip = false
 codegen-units = 16
 
+# Issue #5928: well-known "shared tokio" wrapper crates (#507) are built in
+# the SAME cargo invocation as perry-stdlib-static so cargo unifies their
+# shared dependency graph (tokio, hyper_util, rustls, and even core/std
+# monomorphizations) into identical compilation units. That unification only
+# holds if EVERY crate in that invocation uses the SAME `codegen-units`
+# setting — rustc partitions a crate's monomorphized code into N codegen
+# units based on this value, so two crates compiling the "same" shared
+# dependency with different `codegen-units` end up with differently-sized,
+# differently-partitioned .rcgu.o objects despite sharing an identical
+# crate/feature graph (confirmed empirically: perry-stdlib-static's `core`
+# codegen unit was 551 KB vs an ext crate's 2.4 MB for the identically
+# hash-named unit, before this fix). Without this, macOS's linker (which
+# has no `-multiply_defined suppress` / `-ld_classic` tolerance mode
+# anymore) hits thousands of `ld: duplicate symbol` errors once a program
+# needs 2+ of these wrapper crates simultaneously, because perry's
+# strip-dedup mechanism assumes same-named codegen units are byte-identical
+# and safe to drop duplicates from — an assumption this mismatch violated.
+[profile.release.package.perry-ext-fastify]
+codegen-units = 16
+[profile.release.package.perry-ext-http]
+codegen-units = 16
+[profile.release.package.perry-ext-ioredis]
+codegen-units = 16
+[profile.release.package.perry-ext-net]
+codegen-units = 16
+[profile.release.package.perry-ext-ws]
+codegen-units = 16
+
 # Fast developer profile (#5422). Optimized enough for realistic local runs but
 # without the distribution-grade settings that dominate compile time, so the
 # edit/build loop stays short. Intended local loop:
@@ -300,6 +328,20 @@ codegen-units = 16
 strip = false
 codegen-units = 16
 
+# Issue #5928: mirrors the [profile.release.package.perry-ext-*] block above
+# — see its comment for why matching `codegen-units` across every crate in
+# the "shared tokio" (#507) cargo invocation is required.
+[profile.dist.package.perry-ext-fastify]
+codegen-units = 16
+[profile.dist.package.perry-ext-http]
+codegen-units = 16
+[profile.dist.package.perry-ext-ioredis]
+codegen-units = 16
+[profile.dist.package.perry-ext-net]
+codegen-units = 16
+[profile.dist.package.perry-ext-ws]
+codegen-units = 16
+
 [workspace.package]
 version = "0.5.1236"
 edition = "2021"
diff --git a/crates/perry/src/commands/compile/optimized_libs/driver.rs b/crates/perry/src/commands/compile/optimized_libs/driver.rs
index 05100544f3..2350dd423a 100644
--- a/crates/perry/src/commands/compile/optimized_libs/driver.rs
+++ b/crates/perry/src/commands/compile/optimized_libs/driver.rs
@@ -1069,7 +1069,7 @@ pub(crate) fn build_optimized_libs(
         runtime_bc,
         stdlib_bc,
         extra_bc,
+        prefer_well_known_before_stdlib: !well_known_libs.is_empty(),
         well_known_libs,
-        prefer_well_known_before_stdlib: false,
     }
 }