diff --git a/ports/opencv4/portfile.cmake b/ports/opencv4/portfile.cmake
index 385dd801f3..52dbf9fcda 100644
--- a/ports/opencv4/portfile.cmake
+++ b/ports/opencv4/portfile.cmake
@@ -63,6 +63,10 @@ elseif(VCPKG_TARGET_ARCHITECTURE STREQUAL "arm")
   set(TARGET_IS_ARM 1)
 elseif(VCPKG_TARGET_ARCHITECTURE STREQUAL "x64")
   set(TARGET_IS_X86_64 1)
+elseif(VCPKG_TARGET_IS_EMSCRIPTEN)
+  # wasm32 is not x86: leaving every TARGET_IS_* unset keeps OpenCV off the x86 SSE baseline,
+  # whose runtime guard aborts on wasm. SIMD comes from the wasm HAL configured below.
+  set(TARGET_IS_WASM 1)
 else()
   set(TARGET_IS_X86 1)
 endif()
@@ -409,6 +413,20 @@ if("qt" IN_LIST FEATURES)
   list(APPEND ADDITIONAL_BUILD_FLAGS "-DCMAKE_AUTOMOC=ON")
 endif()
 
+if(VCPKG_TARGET_IS_EMSCRIPTEN)
+  # OpenCV's CPU-optimization machinery assumes a native (x86/ARM) target. On wasm the baseline
+  # and dispatch lists must be empty, otherwise it bakes an x86 SSE baseline whose runtime guard
+  # aborts at startup. Mirrors OpenCV's own platforms/js/build_js.py.
+  list(APPEND ADDITIONAL_BUILD_FLAGS -DCPU_BASELINE= -DCPU_DISPATCH=)
+  if("intrinsics" IN_LIST FEATURES)
+    # SIMD via OpenCV's wasm HAL (intrin_wasm.hpp); -msimd128 makes its builtins available.
+    # CV_ENABLE_INTRINSICS itself is turned on by the "intrinsics" feature.
+    list(APPEND ADDITIONAL_BUILD_FLAGS
+      -DOPENCV_EXTRA_C_FLAGS=-msimd128
+      -DOPENCV_EXTRA_CXX_FLAGS=-msimd128)
+  endif()
+endif()
+
 vcpkg_cmake_configure(
     SOURCE_PATH "${SOURCE_PATH}"
     OPTIONS
diff --git a/ports/opencv4/vcpkg.json b/ports/opencv4/vcpkg.json
index 6ba5b9b0b0..63d28756c1 100644
--- a/ports/opencv4/vcpkg.json
+++ b/ports/opencv4/vcpkg.json
@@ -1,7 +1,7 @@
 {
   "name": "opencv4",
   "version": "4.12.0",
-  "port-version": 4,
+  "port-version": 5,
   "description": "Open Source Computer Vision Library",
   "homepage": "https://opencv.org/",
   "documentation": "https://docs.opencv.org/4.12.0/",
diff --git a/versions/baseline.json b/versions/baseline.json
index f68e9d1a10..c27fb23c86 100644
--- a/versions/baseline.json
+++ b/versions/baseline.json
@@ -7406,7 +7406,7 @@
     },
     "opencv4": {
       "baseline": "4.12.0",
-      "port-version": 4
+      "port-version": 5
     },
     "opendnp3": {
       "baseline": "3.1.2",
diff --git a/versions/o-/opencv4.json b/versions/o-/opencv4.json
index a5fffb9814..3bafa01e7f 100644
--- a/versions/o-/opencv4.json
+++ b/versions/o-/opencv4.json
@@ -1,5 +1,10 @@
 {
   "versions": [
+    {
+      "git-tree": "0e28cd8713d7b810bef28ed0d7859dd761215854",
+      "version": "4.12.0",
+      "port-version": 5
+    },
     {
       "git-tree": "7e25a9ac702b9b94264dc469895c06e82b62d283",
       "version": "4.12.0",