diff --git a/CMakeLists.txt b/CMakeLists.txt
index be6e490c..d90e1341 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -156,6 +156,12 @@ FetchContent_Declare(
         EXCLUDE_FROM_ALL
 )
 
+# CMake >= 4.0 (e.g. the 4.x bundled with Visual Studio 2026) makes any
+# cmake_minimum_required(VERSION < 3.5) a fatal error. Some fetched dependencies still
+# declare such old floors (libzmq: 3.0.2), so raise the policy-version floor for the
+# FetchContent subprojects. Ignored (harmless) on CMake < 3.30, which lacks this variable.
+SET(CMAKE_POLICY_VERSION_MINIMUM 3.5)
+
 # libzmq must be made available BEFORE sls_detector_package for the override above to take effect.
 FetchContent_MakeAvailable(libzmq)
 FetchContent_MakeAvailable(zstd sls_detector_package catch2 hdf5 spdlog httplib)