diff --git a/Buildscr b/Buildscr
index 84465ac0..7fa35fba 100644
--- a/Buildscr
+++ b/Buildscr
@@ -165,15 +165,15 @@ mkdir putty/windows/abuild64
 #
 # For the 32-bit ones, we set a subsystem version of 5.01, which
 # allows the resulting files to still run on Windows XP.
-in putty/windows/build32 with cmake_at_least_3.20 do cmake ../.. -DCMAKE_TOOLCHAIN_FILE=$(cmake_toolchain_clangcl32) -DCMAKE_BUILD_TYPE=Release -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -DPUTTY_LINK_MAPS=ON
+in putty/windows/build32 with cmake_at_least_3.20 do cmake ../.. -DCMAKE_TOOLCHAIN_FILE=$(cmake_toolchain_clangcl32) -DCMAKE_BUILD_TYPE=Release -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -DPUTTY_LINK_MAPS=ON -DCMAKE_C_FLAGS_RELEASE="/MT /O2"
 in putty/windows/build32 with cmake_at_least_3.20 do make -j$(nproc) VERBOSE=1
-in putty/windows/build64 with cmake_at_least_3.20 do cmake ../.. -DCMAKE_TOOLCHAIN_FILE=$(cmake_toolchain_clangcl64) -DCMAKE_BUILD_TYPE=Release -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -DPUTTY_LINK_MAPS=ON
+in putty/windows/build64 with cmake_at_least_3.20 do cmake ../.. -DCMAKE_TOOLCHAIN_FILE=$(cmake_toolchain_clangcl64) -DCMAKE_BUILD_TYPE=Release -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -DPUTTY_LINK_MAPS=ON -DCMAKE_C_FLAGS_RELEASE="/MT /O2"
 in putty/windows/build64 with cmake_at_least_3.20 do make -j$(nproc) VERBOSE=1
 
 # Build experimental Arm Windows binaries.
-in putty/windows/abuild32 with cmake_at_least_3.20 do cmake ../.. -DCMAKE_TOOLCHAIN_FILE=$(cmake_toolchain_clangcl_a32) -DCMAKE_BUILD_TYPE=Release -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -DPUTTY_LINK_MAPS=ON
+in putty/windows/abuild32 with cmake_at_least_3.20 do cmake ../.. -DCMAKE_TOOLCHAIN_FILE=$(cmake_toolchain_clangcl_a32) -DCMAKE_BUILD_TYPE=Release -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -DPUTTY_LINK_MAPS=ON -DCMAKE_C_FLAGS_RELEASE="/MT /O2"
 in putty/windows/abuild32 with cmake_at_least_3.20 do make -j$(nproc) VERBOSE=1
-in putty/windows/abuild64 with cmake_at_least_3.20 do cmake ../.. -DCMAKE_TOOLCHAIN_FILE=$(cmake_toolchain_clangcl_a64) -DCMAKE_BUILD_TYPE=Release -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -DPUTTY_LINK_MAPS=ON
+in putty/windows/abuild64 with cmake_at_least_3.20 do cmake ../.. -DCMAKE_TOOLCHAIN_FILE=$(cmake_toolchain_clangcl_a64) -DCMAKE_BUILD_TYPE=Release -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -DPUTTY_LINK_MAPS=ON -DCMAKE_C_FLAGS_RELEASE="/MT /O2"
 in putty/windows/abuild64 with cmake_at_least_3.20 do make -j$(nproc) VERBOSE=1
 
 # Make a list of the Windows binaries we're going to ship, so that we