diff --git a/ports/webassembly/library.h b/ports/webassembly/library.h
index 47982e0640..21027c1372 100644
--- a/ports/webassembly/library.h
+++ b/ports/webassembly/library.h
@@ -29,3 +29,4 @@
 extern void mp_js_write(const char *str, mp_uint_t len);
 extern int mp_js_ticks_ms(void);
 extern void mp_js_hook(void);
+extern uint32_t mp_js_random_u32(void);
diff --git a/ports/webassembly/library.js b/ports/webassembly/library.js
index f554f681c9..4a17942bb4 100644
--- a/ports/webassembly/library.js
+++ b/ports/webassembly/library.js
@@ -63,4 +63,11 @@ mergeInto(LibraryManager.library, {
             }
         }
     },
+
+    // Node prior to v19 did not expose "crypto" as a global, so make sure it exists.
+    mp_js_random_u32__postset:
+        "if (globalThis.crypto === undefined) { globalThis.crypto = require('crypto'); }",
+
+    mp_js_random_u32: () =>
+        globalThis.crypto.getRandomValues(new Uint32Array(1))[0],
 });
diff --git a/ports/webassembly/mpconfigport.h b/ports/webassembly/mpconfigport.h
index e0d1af0cce..43a029c530 100644
--- a/ports/webassembly/mpconfigport.h
+++ b/ports/webassembly/mpconfigport.h
@@ -49,6 +49,8 @@
 #define MICROPY_FLOAT_IMPL          (MICROPY_FLOAT_IMPL_DOUBLE)
 #define MICROPY_USE_INTERNAL_ERRNO  (1)
 #define MICROPY_USE_INTERNAL_PRINTF (0)
+
+#define MICROPY_PY_RANDOM_SEED_INIT_FUNC (mp_js_random_u32())
 #ifndef MICROPY_VFS
 #define MICROPY_VFS                 (1)
 #endif
@@ -95,3 +97,5 @@ typedef long mp_off_t;
 // _GNU_SOURCE must be defined to get definitions of DT_xxx symbols from dirent.h.
 #define _GNU_SOURCE
 #endif
+
+uint32_t mp_js_random_u32(void);