diff --git a/utils/webassembly/build-foundation.sh b/utils/webassembly/build-foundation.sh
index 76150c269ddcc..d30c045a5fb87 100755
--- a/utils/webassembly/build-foundation.sh
+++ b/utils/webassembly/build-foundation.sh
@@ -12,6 +12,7 @@ mkdir -p $FOUNDATION_BUILD
 cd $FOUNDATION_BUILD
 
 cmake -G Ninja \
+  -DCMAKE_BUILD_TYPE="Release" \
   -DCMAKE_SYSROOT="$WASI_SYSROOT_PATH" \
   -DCMAKE_Swift_COMPILER="$DESTINATION_TOOLCHAIN/usr/bin/swiftc" \
   -DCMAKE_STAGING_PREFIX="$DESTINATION_TOOLCHAIN/usr" \
diff --git a/utils/webassembly/build-xctest.sh b/utils/webassembly/build-xctest.sh
index 88d92b56210ea..e098fe46297d2 100755
--- a/utils/webassembly/build-xctest.sh
+++ b/utils/webassembly/build-xctest.sh
@@ -10,6 +10,7 @@ mkdir -p $BUILD_DIR
 cd $BUILD_DIR
 
 cmake -G Ninja \
+  -DCMAKE_BUILD_TYPE="Release" \
   -DCMAKE_SYSROOT="$WASI_SYSROOT_PATH" \
   -DCMAKE_Swift_COMPILER="$DESTINATION_TOOLCHAIN/usr/bin/swiftc" \
   -DCMAKE_STAGING_PREFIX="$DESTINATION_TOOLCHAIN/usr" \