diff --git a/.github/actions/spelling/expect/expect.txt b/.github/actions/spelling/expect/expect.txt
index 102af4d88f..3d3eff382f 100644
--- a/.github/actions/spelling/expect/expect.txt
+++ b/.github/actions/spelling/expect/expect.txt
@@ -241,6 +241,7 @@ consoletaeftemplates
 consoleuwp
 CONSOLEWINDOWOWNER
 consrv
+consteval
 constexprable
 contentfiles
 conterm
diff --git a/src/inc/LibraryIncludes.h b/src/inc/LibraryIncludes.h
index b9df47f957..728246e1c9 100644
--- a/src/inc/LibraryIncludes.h
+++ b/src/inc/LibraryIncludes.h
@@ -84,8 +84,18 @@
 // {fmt}, a C++20-compatible formatting library
 #pragma warning(push)
 #pragma warning(disable: 4702) // unreachable code
+// Workaround: clang-cl advertises consteval support but fmt's use of it in
+// color.h triggers "call to consteval function is not a constant expression".
+// Hide __cpp_lib_is_constant_evaluated so fmt falls back to the non-consteval path.
+#ifdef __clang__
+#pragma push_macro("__cpp_lib_is_constant_evaluated")
+#undef __cpp_lib_is_constant_evaluated
+#endif
 #include <fmt/compile.h>
 #include <fmt/xchar.h>
+#ifdef __clang__
+#pragma pop_macro("__cpp_lib_is_constant_evaluated")
+#endif
 #pragma warning(pop)
 
 #define USE_INTERVAL_TREE_NAMESPACE
diff --git a/src/project.inc b/src/project.inc
index 152aca2717..cf4a2e048c 100644
--- a/src/project.inc
+++ b/src/project.inc
@@ -35,7 +35,8 @@ USE_NATIVE_EH           = 1
 
 USE_STD_CPP20           = 1
 MSC_WARNING_LEVEL       = /W4 /WX
-USER_C_FLAGS            = $(USER_C_FLAGS) /Zc:preprocessor /fp:contract /utf-8
+USER_C_FLAGS            = $(USER_C_FLAGS) /fp:contract /utf-8
+ZC_PREPROCESSOR         = 1
 
 # -------------------------------------
 # Common Console Includes and Libraries
diff --git a/src/renderer/atlas/pch.h b/src/renderer/atlas/pch.h
index 952d0fb2d7..9d5bc66515 100644
--- a/src/renderer/atlas/pch.h
+++ b/src/renderer/atlas/pch.h
@@ -46,8 +46,18 @@
 // {fmt}, a C++20-compatible formatting library
 #pragma warning(push)
 #pragma warning(disable : 4702) // unreachable code
+// Workaround: clang-cl advertises consteval support but fmt's use of it in
+// color.h triggers "call to consteval function is not a constant expression".
+// Hide __cpp_lib_is_constant_evaluated so fmt falls back to the non-consteval path.
+#ifdef __clang__
+#pragma push_macro("__cpp_lib_is_constant_evaluated")
+#undef __cpp_lib_is_constant_evaluated
+#endif
 #include <fmt/compile.h>
 #include <fmt/xchar.h>
+#ifdef __clang__
+#pragma pop_macro("__cpp_lib_is_constant_evaluated")
+#endif
 #pragma warning(pop)
 
 #include <til.h>