diff --git a/.github/workflows/build-and-test.yml b/.github/workflows/build-and-test.yml
index 1ab63c1159..7210146e88 100644
--- a/.github/workflows/build-and-test.yml
+++ b/.github/workflows/build-and-test.yml
@@ -35,16 +35,19 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
-        compiler: [clang, gcc]
+        compiler: [clang, gcc, gcc-12]
         exclude:
           - os: macos-latest
             compiler: gcc
+          - os: macos-latest
+            compiler: gcc-12
 
     runs-on: ${{ matrix.os }}
 
     # See design.mps.tests.ci.run.posix.
     steps:
     - uses: actions/checkout@v3
+    - run: ${{ matrix.compiler }} --version
     - run: CC=${{ matrix.compiler }} ./configure
     - run: make
     - run: make test
diff --git a/code/arenavm.c b/code/arenavm.c
index 50708e9563..11aca9d1c9 100644
--- a/code/arenavm.c
+++ b/code/arenavm.c
@@ -600,7 +600,7 @@ static Res VMArenaCreate(Arena *arenaReturn, ArgList args)
   VM vm = &vmStruct;
   Chunk chunk;
   mps_arg_s arg;
-  char vmParams[VMParamSize];
+  char vmParams[VMParamSize] = {0}; /* suppress uninitialized warning from GCC 12.2 */
 
   AVER(arenaReturn != NULL);
   AVERT(ArgList, args);
diff --git a/code/ss.c b/code/ss.c
index ce088101f1..2f421b88d4 100644
--- a/code/ss.c
+++ b/code/ss.c
@@ -1,7 +1,7 @@
 /* ss.c: STACK SCANNING
  *
  * $Id$
- * Copyright (c) 2001-2020 Ravenbrook Limited.  See end of file for license.
+ * Copyright (c) 2001-2023 Ravenbrook Limited.  See end of file for license.
  *
  * This scans the mutator's stack and fixes the registers that may
  * contain roots. <design/stack-scan>.
@@ -30,12 +30,32 @@ SRCID(ss, "$Id$");
  * stack by the caller below its other local data, so as long as
  * it does not use something like alloca, the address of the argument
  * is a hot stack pointer.  <design/ss#.sol.stack.hot>.
+ *
  */
 
 ATTRIBUTE_NOINLINE
 void StackHot(void **stackOut)
 {
+ /* GCC 13.1 legitimately complains about us leaking a dangling
+    pointer (-Wdangling-pointer) -- it's exactly what we are trying to
+    do.  Rather that suppressing this warning globally, we use
+    Diagnostic Pragmas
+    <https://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Pragmas.html> to
+    suppress the warning only here. */
+#if CONFIG_BUILD_GC
+#  pragma GCC diagnostic push
+  /* Prevent GCC 11 and GCC 12 producing warnings that they don't know
+     about -Wdangling-pointer and -Wunknown-warning-option. */
+#  pragma GCC diagnostic ignored "-Wpragmas"
+#  pragma GCC diagnostic ignored "-Wunknown-warning-option"
+#  pragma GCC diagnostic ignored "-Wdangling-pointer"
+#endif
+
   *stackOut = &stackOut;
+
+#if CONFIG_BUILD_GC
+#  pragma GCC diagnostic pop
+#endif
 }
 
 
@@ -71,7 +91,7 @@ Res StackScan(ScanState ss, void *stackCold,
 
 /* C. COPYRIGHT AND LICENSE
  *
- * Copyright (C) 2001-2020 Ravenbrook Limited <https://www.ravenbrook.com/>.
+ * Copyright (C) 2001-2023 Ravenbrook Limited <https://www.ravenbrook.com/>.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are