diff --git a/source/main.hon b/source/main.hon
index 9731218..ea2930e 100644
--- a/source/main.hon
+++ b/source/main.hon
@@ -50,11 +50,11 @@ main proc(init process.Init) i32 {
     return command(mem.c_allocator, init.io, init.args) catch |err| {
         if (init.args.values.len > 2) {
             io.print("{s}: infrastructure error: {s}\n", io.stderr(init.io), {
-                init.args.values[2], infrastructure_message(err),
+                init.args.values[2], enummap.get(&infrastructure_messages, err)?,
             }) catch |_| {}
         } else {
             io.print("honey: infrastructure error: {s}\n", io.stderr(init.io), {
-                infrastructure_message(err),
+                enummap.get(&infrastructure_messages, err)?,
             }) catch |_| {}
         }
         return 2
@@ -62,22 +62,20 @@ main proc(init process.Init) i32 {
 }
 
 @hide:file
-infrastructure_message proc(error DriverError) []u8 {
-    return match error {
-        .out_of_memory: "out of memory"
-        .diagnostic_limit_reached: "diagnostic limit reached"
-        .storage_limit_reached: "aggregate storage limit reached"
-        .source_too_large: "source file is too large"
-        .out_of_space: "identifier storage is full"
-        .open_failed: "cannot open source file"
-        .close_failed: "cannot close source file"
-        .not_open_for_reading: "source file is not readable"
-        .read_failed: "cannot read source file"
-        .not_open_for_writing: "output is not writable"
-        .write_failed: "cannot write output"
-        .no_progress: "output writer made no progress"
-    }
-}
+infrastructure_messages :: $enummap.init(DriverError, []u8, {
+    out_of_memory = "out of memory",
+    diagnostic_limit_reached = "diagnostic limit reached",
+    storage_limit_reached = "aggregate storage limit reached",
+    source_too_large = "source file is too large",
+    out_of_space = "identifier storage is full",
+    open_failed = "cannot open source file",
+    close_failed = "cannot close source file",
+    not_open_for_reading = "source file is not readable",
+    read_failed = "cannot read source file",
+    not_open_for_writing = "output is not writable",
+    write_failed = "cannot write output",
+    no_progress = "output writer made no progress",
+})
 
 @hide:file
 command proc(allocator mem.Allocator, runtime io.Io, args process.Args) i32 ! DriverError {
diff --git a/std/enummap/enummap.hon b/std/enummap/enummap.hon
index e7c333b..5fefbe5 100644
--- a/std/enummap/enummap.hon
+++ b/std/enummap/enummap.hon
@@ -1,5 +1,7 @@
 import "@std/meta"
 
+#! keys may be enums or native enum compositions that normalize to an enum, including aliases.
+#! shared variant names follow native composition identity; payload-bearing sums are not enum keys.
 EnumMap proc($E, $V type) type {
     match typeinfo!(E) {
         .enum |info|: return struct {
diff --git a/std/enummap/enummap.test.hon b/std/enummap/enummap.test.hon
index 366277c..3ffed42 100644
--- a/std/enummap/enummap.test.hon
+++ b/std/enummap/enummap.test.hon
@@ -24,3 +24,64 @@ handles_sparse_enum_get test {
     try testing.expect_type(?[]u8, eof)
     try testing.expect_equal(null, eof)
 }
+
+@hide:file
+TestLeftError :: enum {
+    shared
+    left
+    absent_left
+}
+
+@hide:file
+TestRightError :: enum {
+    shared
+    right
+    absent_right
+}
+
+@hide:file
+TestNestedError :: alias (TestLeftError | (TestRightError | TestLeftError))
+
+@hide:file
+TestComposedError :: alias TestNestedError
+
+@hide:file
+composed_values :: $init(TestComposedError, i32, {
+    shared = 11,
+    left = 22,
+    absent_left = 33,
+    right = 44,
+    absent_right = 55,
+})
+
+handles_composed_enum_keys_at_runtime test {
+    names EnumMap(TestComposedError, []u8) :: init({
+        shared = "shared error",
+        left = "left error",
+        right = "right error",
+    })
+    keys [_]TestComposedError :: [
+        TestLeftError.shared,
+        TestLeftError.left,
+        TestRightError.shared,
+        TestRightError.right,
+        TestLeftError.absent_left,
+        TestRightError.absent_right,
+    ]
+    expected [_]?[]u8 :: [
+        "shared error",
+        "left error",
+        "shared error",
+        "right error",
+        null,
+        null,
+    ]
+    expected_values [_]i32 :: [11, 22, 11, 44, 33, 55]
+
+    for keys |key, index| {
+        value :: get(&names, key)
+        try testing.expect_type(?[]u8, value)
+        try testing.expect_equal(expected[index], value)
+        try testing.expect_equal(expected_values[index], get(&composed_values, key)?)
+    }
+}