diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
index 20744b628..ad5b106aa 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
@@ -370,6 +370,13 @@ public class ConfigConstants {
 	 */
 	public static final String CONFIG_KEY_RENAMES = "renames";
 
+	/**
+	 * The "inCoreLimit" key in the "merge section". It's a size limit (bytes) used to
+	 * control a file to be stored in {@code Heap} or {@code LocalFile} during the merge.
+	 * @since 4.9
+	 */
+	public static final String CONFIG_KEY_IN_CORE_LIMIT = "inCoreLimit";
+
 	/**
 	 * The "prune" key
 	 * @since 3.3
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java b/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java
index e77ad953d..92c2bb35a 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java
@@ -85,6 +85,7 @@
 import org.eclipse.jgit.errors.MissingObjectException;
 import org.eclipse.jgit.errors.NoWorkTreeException;
 import org.eclipse.jgit.lib.Config;
+import org.eclipse.jgit.lib.ConfigConstants;
 import org.eclipse.jgit.lib.FileMode;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectInserter;
@@ -272,6 +273,12 @@ public enum MergeFailureReason {
 	 */
 	protected MergeAlgorithm mergeAlgorithm;
 
+	/**
+	 * The size limit (bytes) which controls a file to be stored in {@code Heap} or
+	 * {@code LocalFile} during the merge.
+	 */
+	private int inCoreLimit;
+
 	private static MergeAlgorithm getMergeAlgorithm(Config config) {
 		SupportedAlgorithm diffAlg = config.getEnum(
 				CONFIG_DIFF_SECTION, null, CONFIG_KEY_ALGORITHM,
@@ -279,6 +286,11 @@ private static MergeAlgorithm getMergeAlgorithm(Config config) {
 		return new MergeAlgorithm(DiffAlgorithm.getAlgorithm(diffAlg));
 	}
 
+	private static int getInCoreLimit(Config config) {
+		return config.getInt(
+				ConfigConstants.CONFIG_MERGE_SECTION, ConfigConstants.CONFIG_KEY_IN_CORE_LIMIT, 10 << 20);
+	}
+
 	private static String[] defaultCommitNames() {
 		return new String[] { "BASE", "OURS", "THEIRS" }; //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
 	}
@@ -289,7 +301,9 @@ private static String[] defaultCommitNames() {
 	 */
 	protected ResolveMerger(Repository local, boolean inCore) {
 		super(local);
-		mergeAlgorithm = getMergeAlgorithm(local.getConfig());
+		Config config = local.getConfig();
+		mergeAlgorithm = getMergeAlgorithm(config);
+		inCoreLimit = getInCoreLimit(config);
 		commitNames = defaultCommitNames();
 		this.inCore = inCore;
 
@@ -835,7 +849,7 @@ private File writeMergedFile(MergeResult<RawText> result)
 	private ObjectId insertMergeResult(MergeResult<RawText> result)
 			throws IOException {
 		TemporaryBuffer.LocalFile buf = new TemporaryBuffer.LocalFile(
-				db != null ? nonNullRepo().getDirectory() : null, 10 << 20);
+				db != null ? nonNullRepo().getDirectory() : null, inCoreLimit);
 		try {
 			new MergeFormatter().formatMerge(buf, result,
 					Arrays.asList(commitNames), CHARACTER_ENCODING);