diff --git a/include/verilatedos.h b/include/verilatedos.h
index ae3ceb3bf..0d173cb2f 100644
--- a/include/verilatedos.h
+++ b/include/verilatedos.h
@@ -619,6 +619,8 @@ inline double VL_ROUND(double n) {
 # define VL_CPU_RELAX() asm volatile("lr 0,0" ::: "memory")
 #elif defined(__sparc__)
 # define VL_CPU_RELAX() asm volatile("rd %%ccr, %%g0" ::: "memory")
+#elif defined(__wasm__)  // Wasm has no spin-wait hint, and no inline asm
+# define VL_CPU_RELAX()
 #elif defined(VL_IGNORE_UNKNOWN_ARCH)
 # define VL_CPU_RELAX()
 #else
diff --git a/include/verilatedos_c.h b/include/verilatedos_c.h
index d329da089..6a900b5a9 100644
--- a/include/verilatedos_c.h
+++ b/include/verilatedos_c.h
@@ -65,7 +65,7 @@ double DeltaCpuTime::gettime() VL_MT_SAFE {
                                    | static_cast<uint64_t>(lpUserTime.dwHighDateTime) << 32ULL)
                * 1e-7;
     }
-#else
+#elif !defined(__wasi__)  // WASI has no CLOCK_PROCESS_CPUTIME_ID
     // NOLINTNEXTLINE(cppcoreguidelines-pro-type-member-init)
     timespec ts;
     if (0 == clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts))  // MT-Safe  // LCOV_EXCL_BR_LINE
diff --git a/src/V3Os.cpp b/src/V3Os.cpp
index 7891dd102..62e262779 100644
--- a/src/V3Os.cpp
+++ b/src/V3Os.cpp
@@ -82,7 +82,9 @@ VL_DEFINE_DEBUG_FUNCTIONS;
 # endif
 #else
 # include <sys/time.h>
-# include <sys/wait.h>  // Needed on FreeBSD for WIFEXITED
+# ifndef __wasi__
+#  include <sys/wait.h>  // Needed on FreeBSD for WIFEXITED
+# endif
 # include <unistd.h>  // usleep
 #endif
 // clang-format on
@@ -445,6 +447,12 @@ string V3Os::trueRandom(size_t size) VL_MT_SAFE {
     if (VL_UNCOVERABLE(!BCRYPT_SUCCESS(hr))) {
         v3fatal("Could not acquire random data. Try specifying a key instead.");  // LCOV_EXCL_LINE
     }
+#elif defined(__wasi__)
+    // WASI has no /dev/urandom. getentropy() rejects sizes over 256 bytes,
+    // which is more than any caller asks for, and errors rather than truncates.
+    if (VL_UNCOVERABLE(getentropy(data, size))) {
+        v3fatal("Could not acquire random data. Try specifying a key instead.");  // LCOV_EXCL_LINE
+    }
 #else
     std::ifstream is{"/dev/urandom", std::ios::in | std::ios::binary};
     // This read uses the size of the buffer.
@@ -492,6 +500,11 @@ void V3Os::u_sleep(int64_t usec) {
 // METHODS (sub command)
 
 int V3Os::system(const string& command) {
+#ifdef __wasi__
+    // WASI has no process spawning
+    v3fatal("Running subcommands is not supported on this platform: " << command);
+    return -1;
+#else
     UINFO(1, "Running system: " << command);
     const int ret = ::system(command.c_str());
     if (VL_UNCOVERABLE(ret == -1)) {
@@ -504,6 +517,7 @@ int V3Os::system(const string& command) {
     UINFO(1, command << " returned exit code of " << exit_code);
     UASSERT(exit_code >= 0, "exit code must not be negative");
     return exit_code;
+#endif
 }
 
 void V3Os::selfTest() {
diff --git a/test_regress/t/t_dist_warn_coverage.py b/test_regress/t/t_dist_warn_coverage.py
index 99c84fcae..ffbd902c9 100755
--- a/test_regress/t/t_dist_warn_coverage.py
+++ b/test_regress/t/t_dist_warn_coverage.py
@@ -25,6 +25,7 @@ for s in [
         'Define or directive not defined: `',  # Instead V3ParseImp will warn
         'Expecting define formal arguments. Found:',  # Instead define syntax error
         'Need $SYSTEMC_INCLUDE in environment or when Verilator configured,',  # Would need ./configure
+        'Running subcommands is not supported on this platform:',  # Only hit on e.g. wasm
         'Syntax error: Range \':\', \'+:\' etc are not allowed in the instance',  # Instead get syntax error
         'dynamic new() not expected in this context (expected under an assign)',  # Instead get syntax error
         'exited with',  # Is hit; driver.py filters out