diff --git a/impl.c b/impl.c
index 47ba16bc..855343de 100644
--- a/impl.c
+++ b/impl.c
@@ -964,7 +964,9 @@ static void check_host_instruction_availability()
 
     /* Then report all of the ones that aren't available */
     // "WARNING: Host does not support the '%s' instruction"
+#if !defined( __EMSCRIPTEN__ )  /* (wasm has no host x86 instructions) */
     if (!sysblk.have_PCLMULQDQ) WRMSG( HHC00026, "W", "PCLMULQDQ" );
+#endif
 //  if (!sysblk.have_XXXXXXXXX) WRMSG( HHC00026, "W", "XXXXXXXXX" );
 }
 
@@ -1274,8 +1276,15 @@ int     rc, maxprio, minprio;
        flag needs to be set BEFORE logger_init gets called since the
        "logger_logfile_write()" function relies on its setting.
     */
+#if !defined( __EMSCRIPTEN__ )
     if (!isatty(STDERR_FILENO) && !isatty(STDOUT_FILENO))
         sysblk.NoUI_mode = 1;       /* Leave -n intact */
+#else
+    /* wasm: stdout/stderr are never ttys (Node pipes, browser console),
+       but the embedder (src/wasm/wasm_main.c) is a herclin-style log
+       callback user, not NoUI mode: impl() must return before the rc
+       file runs, and do_shutdown_now() must not call exit() itself. */
+#endif
 
     /* Initialize panel colors */
     set_panel_colors();
@@ -1456,7 +1465,15 @@ int     rc, maxprio, minprio;
 
     /* Set default TCP keepalive values */
 
-#if !defined( HAVE_BASIC_KEEPALIVE )
+#if defined( __EMSCRIPTEN__ )
+
+    /* No TCP keepalive in wasm (hostopts.h undefines the HAVE_*_KEEPALIVE
+       values; the 3270 connections are in-process, see wasmsock.c) */
+    sysblk.kaidle = 0;
+    sysblk.kaintv = 0;
+    sysblk.kacnt  = 0;
+
+#elif !defined( HAVE_BASIC_KEEPALIVE )
 
     WARNING("TCP keepalive headers not found; check configure.ac")
     WARNING("TCP keepalive support will NOT be generated")
@@ -1616,6 +1633,7 @@ int     rc, maxprio, minprio;
        to SIGTERM.
     */
 
+#if !defined( __EMSCRIPTEN__ )  /* (no signals reach a wasm module) */
     /* Register the SIGINT handler */
     if (signal( SIGINT, sigint_handler ) == SIG_ERR)
     {
@@ -1633,6 +1651,7 @@ int     rc, maxprio, minprio;
         delayed_exit( -1 );
         return 1;
     }
+#endif /* !defined( __EMSCRIPTEN__ ) */
 
 #if defined( _MSVC_ )
     /* Register the Window console ctrl handlers */
@@ -1682,7 +1701,7 @@ int     rc, maxprio, minprio;
     }
 #endif
 
-#if defined( HAVE_DECL_SIGPIPE ) && HAVE_DECL_SIGPIPE
+#if defined( HAVE_DECL_SIGPIPE ) && HAVE_DECL_SIGPIPE && !defined( __EMSCRIPTEN__ )
     /* Ignore the SIGPIPE signal, otherwise Hercules may terminate with
        Broken Pipe error if the printer driver writes to a closed pipe */
     if (signal( SIGPIPE, SIG_IGN ) == SIG_ERR)