diff --git a/code/config.h b/code/config.h
index aa9b70c7cc..987f4a8034 100644
--- a/code/config.h
+++ b/code/config.h
@@ -710,6 +710,23 @@
 #define WB_DEFER_HIT   1  /* boring scans after barrier hit */
 
 
+/* Apple Hardened Runtime
+ *
+ * .hardened-runtime: On Apple Silicon, applications may be compiled
+ * with Hardened Runtime enabled. These applications have restricted
+ * capabilities: in particular, unless the "Allow Unsigned Executable
+ * Memory Entitlement" is enabled, these applications cannot create
+ * memory that is simultaneously writable and executable. Attempts to
+ * do so using mmap() and mprotect() fail with EACCES.
+ *
+ * See <https://developer.apple.com/documentation/security/hardened_runtime>
+ */
+#if defined(MPS_OS_XC) && defined(MPS_ARCH_A6)
+#define MAYBE_HARDENED_RUNTIME 1
+#else
+#define MAYBE_HARDENED_RUNTIME 0
+#endif
+
 #endif /* config_h */
 
 
diff --git a/code/protix.c b/code/protix.c
index 3c9f520398..2f1ad1f62e 100644
--- a/code/protix.c
+++ b/code/protix.c
@@ -41,13 +41,21 @@
 
 #include "vm.h"
 
+#include <errno.h>
 #include <limits.h>
+#include <signal.h> /* sig_atomic_t */
 #include <stddef.h>
 #include <sys/mman.h>
 #include <sys/types.h>
 
 SRCID(protix, "$Id$");
 
+
+/* Value for memory protection corresponding to AccessSetEMPTY. */
+
+static sig_atomic_t prot_all = PROT_READ | PROT_WRITE | PROT_EXEC;
+
+
 /* ProtSet -- set protection
  *
  * This is just a thin veneer on top of mprotect(2).
@@ -55,7 +63,7 @@ SRCID(protix, "$Id$");
 
 void ProtSet(Addr base, Addr limit, AccessSet mode)
 {
-  int flags;
+  int flags, result;
 
   AVER(sizeof(size_t) == sizeof(Addr));
   AVER(base < limit);
@@ -82,7 +90,7 @@ void ProtSet(Addr base, Addr limit, AccessSet mode)
     flags = PROT_READ | PROT_EXEC;
     break;
   case AccessSetEMPTY:
-    flags = PROT_READ | PROT_WRITE | PROT_EXEC;
+    flags = prot_all;
     break;
   default:
     NOTREACHED;
@@ -90,7 +98,15 @@ void ProtSet(Addr base, Addr limit, AccessSet mode)
   }
 
   /* .assume.mprotect.base */
-  if(mprotect((void *)base, (size_t)AddrOffset(base, limit), flags) != 0)
+  result = mprotect((void *)base, (size_t)AddrOffset(base, limit), flags);
+  if (MAYBE_HARDENED_RUNTIME && result != 0 && errno == EACCES
+      && (flags & PROT_WRITE) && (flags & PROT_EXEC))
+  {
+    /* See <config.h#hardened-runtime>. */
+    prot_all = PROT_READ | PROT_WRITE;
+    result = mprotect((void *)base, (size_t)AddrOffset(base, limit), flags & prot_all);
+  }
+  if (result != 0)
     NOTREACHED;
 }
 
diff --git a/code/vmix.c b/code/vmix.c
index 418c26f700..941939f170 100644
--- a/code/vmix.c
+++ b/code/vmix.c
@@ -47,6 +47,7 @@
 #include "vm.h"
 
 #include <errno.h> /* errno */
+#include <signal.h> /* sig_atomic_t */
 #include <sys/mman.h> /* see .feature.li in config.h */
 #include <sys/types.h> /* mmap, munmap */
 #include <unistd.h> /* getpagesize */
@@ -156,11 +157,17 @@ void VMFinish(VM vm)
 }
 
 
+/* Value to use for protection of newly allocated pages. */
+
+static sig_atomic_t vm_prot = PROT_READ | PROT_WRITE | PROT_EXEC;
+
+
 /* VMMap -- map the given range of memory */
 
 Res VMMap(VM vm, Addr base, Addr limit)
 {
   Size size;
+  void *result;
 
   AVERT(VM, vm);
   AVER(sizeof(void *) == sizeof(Addr));
@@ -172,11 +179,19 @@ Res VMMap(VM vm, Addr base, Addr limit)
 
   size = AddrOffset(base, limit);
 
-  if(mmap((void *)base, (size_t)size,
-          PROT_READ | PROT_WRITE | PROT_EXEC,
-          MAP_ANON | MAP_PRIVATE | MAP_FIXED,
-          -1, 0)
-     == MAP_FAILED) {
+  result = mmap((void *)base, (size_t)size, vm_prot,
+                MAP_ANON | MAP_PRIVATE | MAP_FIXED,
+                -1, 0);
+  if (MAYBE_HARDENED_RUNTIME && result == MAP_FAILED && errno == EACCES
+      && (vm_prot & PROT_WRITE) && (vm_prot & PROT_EXEC))
+  {
+    /* See <config.h#hardened-runtime>. */
+    vm_prot = PROT_READ | PROT_WRITE;
+    result = mmap((void *)base, (size_t)size, vm_prot,
+                  MAP_ANON | MAP_PRIVATE | MAP_FIXED,
+                  -1, 0);
+  }
+  if (result == MAP_FAILED) {
     AVER(errno == ENOMEM); /* .assume.mmap.err */
     return ResMEMORY;
   }