diff --git a/src/oryx/NOTES.md b/src/oryx/NOTES.md
index ec69ec059..9500db251 100644
--- a/src/oryx/NOTES.md
+++ b/src/oryx/NOTES.md
@@ -5,3 +5,9 @@
 See [supportedPlatformVersions.md](https://github.com/microsoft/Oryx/blob/main/doc/supportedPlatformVersions.md) on the Oryx repository for supported platforms.  Notably, `oryx` does not support Debian "jammy".
 
 `bash` is required to execute the `install.sh` script.
+
+## Pinned Oryx Commit
+
+The Oryx repository is pinned to commit `689fdef61a38802f1e1deda40be5933cc75e3631` (2026-01-13) to avoid a breaking change introduced in commit `21c559437d69cb43fd9b34f01f68c43ea4bce318` that added a `GetFileSize` method to `ISourceRepo` without updating the `MemorySourceRepo` test mock implementation, causing compilation failures.
+
+This pin should be reviewed periodically and updated once the upstream issue is resolved.
diff --git a/src/oryx/install.sh b/src/oryx/install.sh
index cf67db6b1..f70a156ee 100755
--- a/src/oryx/install.sh
+++ b/src/oryx/install.sh
@@ -173,21 +173,24 @@ fi
 BUILD_SCRIPT_GENERATOR=/usr/local/buildscriptgen
 ORYX=/usr/local/oryx
 GIT_ORYX=/opt/tmp/oryx-repo
+# Pin to commit 689fdef61a38802f1e1deda40be5933cc75e3631 (before breaking change on 2026-01-13)
+# See: https://github.com/microsoft/Oryx/commit/21c559437d69cb43fd9b34f01f68c43ea4bce318
+ORYX_PINNED_COMMIT="689fdef61a38802f1e1deda40be5933cc75e3631"
 
 mkdir -p ${BUILD_SCRIPT_GENERATOR}
 mkdir -p ${ORYX}
 
-git clone --depth=1 https://github.com/microsoft/Oryx $GIT_ORYX
+git clone https://github.com/microsoft/Oryx $GIT_ORYX
+cd $GIT_ORYX
+git checkout $ORYX_PINNED_COMMIT
 
 if [[ "${PINNED_SDK_VERSION}" != "" ]]; then
-    cd $GIT_ORYX
     dotnet new globaljson --sdk-version ${PINNED_SDK_VERSION}
 fi
 
 SOLUTION_FILE_NAME="Oryx.sln"
 echo "Building solution '$SOLUTION_FILE_NAME'..."
 
-cd $GIT_ORYX
 ${DOTNET_BINARY} build "$SOLUTION_FILE_NAME" -c Debug
 
 ${DOTNET_BINARY} publish -property:ValidateExecutableReferencesMatchSelfContained=false -r linux-x64 -o ${BUILD_SCRIPT_GENERATOR} -c Release $GIT_ORYX/src/BuildScriptGeneratorCli/BuildScriptGeneratorCli.csproj --self-contained true