diff --git a/scripts/download-core.sh b/scripts/download-core.sh
index 8c1d7b22..4d0ab6c9 100755
--- a/scripts/download-core.sh
+++ b/scripts/download-core.sh
@@ -94,50 +94,58 @@ check_release_notes() {
     grep -Fqi "$REALM_CORE_VERSION RELEASE NOTES" "$@"
 }
 
-if [ ! -e "vendor/$CORE_DIR" ]; then
-    download_core $CORE_DIR $REALM_CORE_VERSION $CORE_DOWNLOAD_FILE core "tar -xzf" core
-elif [ -d "vendor/$CORE_DIR" -a -d ../realm-core -a ! -L "vendor/$CORE_DIR" ]; then
-    # Allow newer versions than expected for local builds as testing
-    # with unreleased versions is one of the reasons to use a local build
-    if ! check_release_notes "vendor/$CORE_DIR/CHANGELOG.txt"; then
-        die "Local build of core is out of date."
-    else
-        echo "The core library seems to be up to date."
-    fi
-elif [ ! -L "vendor/$CORE_DIR" ]; then
-    echo "vendor/$CORE_DIR is not a symlink. Deleting..."
-    rm -rf "vendor/$CORE_DIR"
-    download_core $CORE_DIR $REALM_CORE_VERSION $CORE_DOWNLOAD_FILE core "tar -xzf" core
-# With a prebuilt version we only want to check the first non-empty
-# line so that checking out an older commit will download the
-# appropriate version of core if the already-present version is too new
-elif ! grep -m 1 . "vendor/$CORE_DIR/CHANGELOG.txt" | check_release_notes; then
-    download_core $CORE_DIR $REALM_CORE_VERSION $CORE_DOWNLOAD_FILE core "tar -xzf" core
-else
-    echo "The core library seems to be up to date."
-fi
-
-if [ -n "$SYNC_DOWNLOAD_FILE" ];then
-    if [ ! -e "vendor/$SYNC_DIR" ]; then
-        download_core $SYNC_DIR $REALM_SYNC_VERSION $SYNC_DOWNLOAD_FILE sync "$SYNC_EXTRACT" $EXTRACTED_DIR
-    elif [ -d "vendor/$SYNC_DIR" -a -d ../realm-sync -a ! -L "vendor/$SYNC_DIR" ]; then
+if [ -z "$REALM_CORE_PREFIX" ]; then
+    if [ ! -e "vendor/$CORE_DIR" ]; then
+        download_core $CORE_DIR $REALM_CORE_VERSION $CORE_DOWNLOAD_FILE core "tar -xzf" core
+    elif [ -d "vendor/$CORE_DIR" -a -d ../realm-core -a ! -L "vendor/$CORE_DIR" ]; then
         # Allow newer versions than expected for local builds as testing
         # with unreleased versions is one of the reasons to use a local build
-        if ! check_release_notes "vendor/$SYNC_DIR/version.txt"; then
-            die "Local build of sync is out of date."
+        if ! check_release_notes "vendor/$CORE_DIR/CHANGELOG.txt"; then
+            die "Local build of core is out of date."
         else
-            echo "The sync library seems to be up to date."
+            echo "The core library seems to be up to date."
         fi
-    elif [ ! -L "vendor/$SYNC_DIR" ]; then
-        echo "vendor/$SYNC_DIR is not a symlink. Deleting..."
-        rm -rf "vendor/$SYNC_DIR"
-        download_core $SYNC_DIR $REALM_SYNC_VERSION $SYNC_DOWNLOAD_FILE sync "$SYNC_EXTRACT" $EXTRACTED_DIR
+    elif [ ! -L "vendor/$CORE_DIR" ]; then
+        echo "vendor/$CORE_DIR is not a symlink. Deleting..."
+        rm -rf "vendor/$CORE_DIR"
+        download_core $CORE_DIR $REALM_CORE_VERSION $CORE_DOWNLOAD_FILE core "tar -xzf" core
     # With a prebuilt version we only want to check the first non-empty
     # line so that checking out an older commit will download the
     # appropriate version of core if the already-present version is too new
-    elif ! grep -m 1 . "vendor/$SYNC_DIR/version.txt"; then
-        download_core $SYNC_DIR $REALM_SYNC_VERSION $SYNC_DOWNLOAD_FILE sync "$SYNC_EXTRACT" $EXTRACTED_DIR
+    elif ! grep -m 1 . "vendor/$CORE_DIR/CHANGELOG.txt" | check_release_notes; then
+        download_core $CORE_DIR $REALM_CORE_VERSION $CORE_DOWNLOAD_FILE core "tar -xzf" core
     else
-        echo "The sync library seems to be up to date."
+        echo "The core library seems to be up to date."
     fi
+else
+    echo "Skipping core the download because REALM_CORE_PREFIX is defined."
+fi
+
+if [ -z "$REALM_SYNC_PREFIX" ]; then
+    if [ -n "$SYNC_DOWNLOAD_FILE" ];then
+        if [ ! -e "vendor/$SYNC_DIR" ]; then
+            download_core $SYNC_DIR $REALM_SYNC_VERSION $SYNC_DOWNLOAD_FILE sync "$SYNC_EXTRACT" $EXTRACTED_DIR
+        elif [ -d "vendor/$SYNC_DIR" -a -d ../realm-sync -a ! -L "vendor/$SYNC_DIR" ]; then
+            # Allow newer versions than expected for local builds as testing
+            # with unreleased versions is one of the reasons to use a local build
+            if ! check_release_notes "vendor/$SYNC_DIR/version.txt"; then
+                die "Local build of sync is out of date."
+            else
+                echo "The sync library seems to be up to date."
+            fi
+        elif [ ! -L "vendor/$SYNC_DIR" ]; then
+            echo "vendor/$SYNC_DIR is not a symlink. Deleting..."
+            rm -rf "vendor/$SYNC_DIR"
+            download_core $SYNC_DIR $REALM_SYNC_VERSION $SYNC_DOWNLOAD_FILE sync "$SYNC_EXTRACT" $EXTRACTED_DIR
+        # With a prebuilt version we only want to check the first non-empty
+        # line so that checking out an older commit will download the
+        # appropriate version of core if the already-present version is too new
+        elif ! grep -m 1 . "vendor/$SYNC_DIR/version.txt"; then
+            download_core $SYNC_DIR $REALM_SYNC_VERSION $SYNC_DOWNLOAD_FILE sync "$SYNC_EXTRACT" $EXTRACTED_DIR
+        else
+            echo "The sync library seems to be up to date."
+        fi
+    fi
+else
+    echo "Skipping the sync download because REALM_SYNC_PREFIX is defined."
 fi