diff --git a/tools/build_rules/select.bzl b/tools/build_rules/select.bzl
index 7e6501c..45ba612 100644
--- a/tools/build_rules/select.bzl
+++ b/tools/build_rules/select.bzl
@@ -3,6 +3,11 @@
 # quickly find issues where something new isn't handled.
 # It will also make adding ORs when it makes sense easy to do nicely.
 
+# TODO(james): Decide what to do about webassembly/emscripten CPU and
+# compiler configurations. Bazel does not seem to handle the fact that a select
+# statement may not logically need to be evaluated for certain configurations
+# (e.g., most targets can't be build for --cpu=web, so handling "web" in the
+# cpu_select should notionally be unnecessary).
 all_cpus = [
     "amd64",
     "roborio",
@@ -47,6 +52,7 @@
     '@//tools:cpu_armhf': values['armhf'],
     '@//tools:cpu_cortex_m4f': values['cortex-m'],
     '@//tools:cpu_cortex_m4f_k22': values['cortex-m'],
+    '@//tools:cpu_web': None,
   })
 
 """A select wrapper for address space sizes.
@@ -67,6 +73,7 @@
     '@//tools:cpu_armhf': values['32'],
     '@//tools:cpu_cortex_m4f': values['32'],
     '@//tools:cpu_cortex_m4f_k22': values['32'],
+    '@//tools:cpu_web': None,
   })
 
 """A select wrapper for compilers.
@@ -85,4 +92,5 @@
   return select({
     '@//tools:compiler_gcc': values['gcc'],
     '@//tools:compiler_clang': values['clang'],
+    '@//tools:compiler_emscripten': None,
   })