diff --git a/ps2xRuntime/CMakeLists.txt b/ps2xRuntime/CMakeLists.txt
index e4dc1956d..7d6e6a8c7 100644
--- a/ps2xRuntime/CMakeLists.txt
+++ b/ps2xRuntime/CMakeLists.txt
@@ -552,6 +552,9 @@ if(PS2X_IS_VITA)
     endif()
 endif()
 
+# PUBLIC, so recompiled game code linking against ps2_runtime inherits it.
+EnableX86SimdBaseline(ps2_runtime)
+
 if(CMAKE_BUILD_TYPE STREQUAL "Release" OR CMAKE_BUILD_TYPE STREQUAL "RelWithDebInfo")
     EnableFastReleaseMode(ps2_runtime)
     EnableFastReleaseMode(ps2EntryRunner)
diff --git a/ps2xRuntime/cmake/ReleaseMode.cmake b/ps2xRuntime/cmake/ReleaseMode.cmake
index 92ef0d54d..511fb787d 100644
--- a/ps2xRuntime/cmake/ReleaseMode.cmake
+++ b/ps2xRuntime/cmake/ReleaseMode.cmake
@@ -2,6 +2,21 @@ include(CheckIPOSupported)
 
 check_ipo_supported(RESULT IPO_SUPPORTED OUTPUT IPO_ERROR)
 
+# SSE4.1 is required to compile, not an optimisation: ps2_runtime.h includes
+# <smmintrin.h> and the recompiler emits SSE4.1-only intrinsics. GCC and Clang
+# default to the SSE2 baseline, so those TUs fail without this. Kept out of
+# EnableFastReleaseMode because it applies to every configuration, not just
+# Release.
+function(EnableX86SimdBaseline TargetName)
+    if(MSVC)
+        return()
+    endif()
+    if(NOT CMAKE_SYSTEM_PROCESSOR MATCHES "^(x86_64|AMD64|amd64|i[3-6]86|x86)$")
+        return()
+    endif()
+    target_compile_options(${TargetName} PUBLIC -msse4.1)
+endfunction()
+
 function(EnableFastReleaseMode TargetName)
     message("> Enabling optimization for: ${TargetName}")
     if(MSVC)