diff --git a/toolchains/emscripten/defs.mak b/toolchains/emscripten/defs.mak
index a3b25d4e..c5f21ea5 100644
--- a/toolchains/emscripten/defs.mak
+++ b/toolchains/emscripten/defs.mak
@@ -20,6 +20,15 @@ MAKE_WASM = 1
 # Emscripten linker flags.
 # The link step runs from the magic/ subdirectory, so embed-file paths
 # are relative to that directory (../scmos, ../windows/...).
+#
+# INCOMING_MODULE_JS_API is emscripten's default list plus `wasmBinary`.
+# Our JS loaders (npm/examples/*.js) pass Module.wasmBinary to embed the .wasm,
+# but emscripten 6.0.2 dropped wasmBinary (and a batch of GL/SDL members) from
+# the default INCOMING_MODULE_JS_API. With ASSERTIONS=1 that turns into a hard
+# runtime abort: "`Module.wasmBinary` was supplied but `wasmBinary` not included
+# in INCOMING_MODULE_JS_API". We spell out the full default list (so external
+# consumers passing locateFile/arguments/etc. keep working) and re-add
+# wasmBinary. Keep this in sync with emscripten's default if it grows.
 TOP_EXTRA_LIBS += \
     -sWASM=1 \
     -sMODULARIZE=1 \
@@ -27,6 +36,7 @@ TOP_EXTRA_LIBS += \
     -sUSE_ZLIB=1 \
     -sEXPORTED_FUNCTIONS=_magic_wasm_init,_magic_wasm_run_command,_magic_wasm_source_file,_magic_wasm_update \
     -sEXPORTED_RUNTIME_METHODS=cwrap,ccall,FS,setValue,getValue \
+    -sINCOMING_MODULE_JS_API=ENVIRONMENT,arguments,canvas,dynamicLibraries,elementPointerLock,instantiateWasm,locateFile,monitorRunDependencies,noExitRuntime,noInitialRun,onAbort,onExit,onRuntimeInitialized,postRun,preInit,preRun,print,printErr,setStatus,statusMessage,stderr,stdin,stdout,thisProgram,wasm,websocket,wasmBinary \
     -sALLOW_MEMORY_GROWTH=1 \
     -sINITIAL_MEMORY=67108864 \
     -Wl,-z,stack-size=10485760 \