diff --git a/build.zig b/build.zig
index 5745498..f4b1783 100644
--- a/build.zig
+++ b/build.zig
@@ -1074,6 +1074,25 @@ pub fn build(b: *std.Build) void {
     // Charts read straight out of a .zip, and the aux files that travel with
     // them: pure over std, so each tests alone.
     _ = addPkgTest(b, test_step, "src/zipsrc.zig", target, optimize, &.{});
+    // src/chart.zig holds tests no other step collects: the engine imports it
+    // as a module, and a module import leaves another module's test blocks out.
+    // It needs libc for portray's embedded Lua.
+    addPkgTest(b, test_step, "src/chart.zig", target, optimize, &.{
+        .{ .name = "s57", .module = s57_mod },
+        .{ .name = "s101", .module = s101_mod },
+        .{ .name = "tiles", .module = tiles_mod },
+        .{ .name = "scene", .module = scene_mod },
+        .{ .name = "render", .module = render_mod },
+        .{ .name = "portray", .module = portray_mod },
+        .{ .name = "sprite", .module = sprite_mod },
+        .{ .name = "catalog", .module = catalog_embed },
+        .{ .name = "zipsrc", .module = zipsrc_mod },
+        .{ .name = "auxfiles", .module = auxfiles_mod },
+        .{ .name = "style", .module = style_mod },
+        .{ .name = "coverage", .module = coverage_mod },
+        .{ .name = "compose", .module = compose_mod },
+        .{ .name = "raster", .module = raster_mod },
+    }).link_libc = true;
     _ = addPkgTest(b, test_step, "src/auxfiles.zig", target, optimize, &.{});
     // Geometry core for the cross-band composition. No longer std-only: plane.zig
     // reads its partition tuning/stats valves via std.c.getenv, so the test binary
diff --git a/src/chart.zig b/src/chart.zig
index 42ac17c..8bacb9b 100644
--- a/src/chart.zig
+++ b/src/chart.zig
@@ -39,6 +39,17 @@ const zipsrc = @import("zipsrc"); // charts read straight out of a .zip
 const auxfiles = @import("auxfiles"); // the text and pictures a cell points at
 const raster_pkg = @import("raster"); // picture charts, for the inventory probe
 
+// lua_shim.c is compiled into every binary that links the portray module, and
+// it references 30 symbols exported from portray.zig, s101/catalogue.zig and
+// portray/rules_embed.zig. Zig emits an export only after analyzing the
+// declaration, and the tests in this file reach none of the three, so without
+// these references a test binary links lua_shim.o against 30 undefined
+// symbols. rules_embed follows from portray.
+comptime {
+    _ = portray;
+    _ = catalogue;
+}
+
 // c_allocator, not smp_allocator: smp's per-CPU slab freelists never return
 // pages to the OS, so a long-lived host process's footprint ratchets up to the
 // worst transient peak (compose bursts) and never recovers. libc malloc frees