diff --git a/hmacros.h b/hmacros.h
index 77cde1a2..554f0338 100644
--- a/hmacros.h
+++ b/hmacros.h
@@ -195,6 +195,33 @@ typedef char _CASSERT_PASTE( assertion_failed_ ## file, line )[ 2 * !!(cond) - 1
   #define  read_pipe(f,b,n)     recv(f,b,n,0)
   #define  write_pipe(f,b,n)    send(f,b,(int)n,0)
   #define  close_pipe(f)        closesocket(f)
+#elif defined( __EMSCRIPTEN__ )
+  /* Emscripten pipes never block: read() of an empty pipe gives
+     EAGAIN (legacy FS) or 0 (WasmFS). RECV_PIPE_SIGNAL expects a
+     blocking 1-byte read after the flag was seen set (the writer
+     sets the flag before it writes the byte), so poll and retry.  */
+  #define  create_pipe(f)       pipe(f)
+  #define  read_pipe(f,b,n)     hw_read_pipe(f,b,n)
+  #define  write_pipe(f,b,n)    write(f,b,n)
+  #define  close_pipe(f)        close(f)
+  static inline ssize_t hw_read_pipe( int fd, void* buf, size_t n )
+  {
+      int tries;
+      ssize_t rc = -1;
+      for (tries = 0; tries < 5000; tries++)  /* (about 5 seconds) */
+      {
+          struct pollfd pfd;
+          rc = read( fd, buf, n );
+          if (rc > 0)
+              return rc;
+          if (rc < 0 && errno != EAGAIN && errno != EWOULDBLOCK && errno != EINTR)
+              return rc;
+          pfd.fd = fd; pfd.events = POLLIN; pfd.revents = 0;
+          poll( &pfd, 1, 1 );
+          usleep( 1000 );
+      }
+      return rc;
+  }
 #else
   #define  create_pipe(f)       pipe(f)
   #define  read_pipe(f,b,n)     read(f,b,n)
@@ -519,7 +546,12 @@ typedef int CMPFUNC(const void*, const void*);
 /*-------------------------------------------------------------------*/
 /*      CRASH                       (with hopefully a dump)          */
 /*-------------------------------------------------------------------*/
+#if defined( __EMSCRIPTEN__ )
+/* A store to address 0 does not trap in wasm linear memory.         */
+#define CRASH()         __builtin_trap()
+#else
 #define CRASH()         do { BYTE* p=NULL; *p=0; } while (0)
+#endif
 
 /*-------------------------------------------------------------------*/
 /*      Perform standard utility initialization                      */