diff --git a/.github/workflows/test-compile.yml b/.github/workflows/test-compile.yml
index fe6a43634..3e2ac34c9 100644
--- a/.github/workflows/test-compile.yml
+++ b/.github/workflows/test-compile.yml
@@ -47,8 +47,8 @@ jobs:
           - 'clang-14'
           - 'gcc-11'
           # newest, make sure to update maximum standard step to match
-          - 'clang-19'
-          - 'gcc-14'
+          - 'clang-22'
+          - 'gcc-15'
         include:
           # macOS x86
           - os: macos-15-intel
@@ -96,7 +96,7 @@ jobs:
 
       # maximum standard, only on newest compilers
       - name: Build C++26
-        if: ${{ matrix.compiler == 'clang-19' || matrix.compiler == 'gcc-14' }}
+        if: ${{ matrix.compiler == 'clang-19' || matrix.compiler == 'clang-22' || matrix.compiler == 'gcc-15' }}
         shell: bash
         run: |
           make config-$CC_SHORT
diff --git a/kernel/fmt.cc b/kernel/fmt.cc
index 200e7e5ce..15179a75a 100644
--- a/kernel/fmt.cc
+++ b/kernel/fmt.cc
@@ -804,8 +804,10 @@ std::string Fmt::render() const
 								buf += 'X';
 							else if (has_z)
 								buf += 'Z';
-							else
-								buf += (part.hex_upper ? "0123456789ABCDEF" : "0123456789abcdef")[subvalue.as_int()];
+							else {
+								const char *digits = part.hex_upper ? "0123456789ABCDEF" : "0123456789abcdef";
+								buf += digits[subvalue.as_int()];
+							}
 						}
 					} else if (part.base == 10) {
 						if (part.show_base)