diff --git a/src/oryx/install.sh b/src/oryx/install.sh
index cf67db6b1..06070027f 100755
--- a/src/oryx/install.sh
+++ b/src/oryx/install.sh
@@ -179,6 +179,39 @@ mkdir -p ${ORYX}
 
 git clone --depth=1 https://github.com/microsoft/Oryx $GIT_ORYX
 
+# Patch MemorySourceRepo to implement ISourceRepo.GetFileSize method
+# This fixes a breaking interface change introduced in upstream Oryx
+# See: https://github.com/microsoft/Oryx/commit/21c559437d69cb43fd9b34f01f68c43ea4bce318
+MEMORY_SOURCE_REPO_FILE="$GIT_ORYX/tests/Detector.Tests/MemorySourceRepo.cs"
+if [ -f "$MEMORY_SOURCE_REPO_FILE" ]; then
+    # Check if GetFileSize is already implemented
+    if ! grep -q "GetFileSize" "$MEMORY_SOURCE_REPO_FILE"; then
+        echo "Patching MemorySourceRepo to add GetFileSize implementation..."
+        # Add GetFileSize implementation before the GetGitCommitId method
+        sed -i '/public string GetGitCommitId()/i\
+        public long? GetFileSize(params string[] paths)\
+        {\
+            var path = Path.Combine(paths);\
+            if (!pathsToFiles.ContainsKey(path))\
+            {\
+                return null;\
+            }\
+            var content = pathsToFiles[path];\
+            return content?.Length;\
+        }\
+' "$MEMORY_SOURCE_REPO_FILE"
+        
+        # Verify the patch was applied
+        if grep -q "GetFileSize" "$MEMORY_SOURCE_REPO_FILE"; then
+            echo "Successfully patched MemorySourceRepo"
+        else
+            echo "Warning: Failed to patch MemorySourceRepo - build may fail"
+        fi
+    else
+        echo "MemorySourceRepo already has GetFileSize implementation, skipping patch"
+    fi
+fi
+
 if [[ "${PINNED_SDK_VERSION}" != "" ]]; then
     cd $GIT_ORYX
     dotnet new globaljson --sdk-version ${PINNED_SDK_VERSION}