diff --git a/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties b/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
index 51e44fd77..cdb2be151 100644
--- a/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
+++ b/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
@@ -87,6 +87,7 @@ cannotReadBlob=Cannot read blob {0}
 cannotReadCommit=Cannot read commit {0}
 cannotReadFile=Cannot read file {0}
 cannotReadHEAD=cannot read HEAD: {0} {1}
+cannotReadIndex=The index file {0} exists but cannot be read
 cannotReadObject=Cannot read object
 cannotReadObjectsPath=Cannot read {0}/{1}: {2}
 cannotReadTree=Cannot read tree {0}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCache.java b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCache.java
index 92cdf391c..387d8ce73 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCache.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCache.java
@@ -63,6 +63,7 @@
 import java.util.List;
 
 import org.eclipse.jgit.errors.CorruptObjectException;
+import org.eclipse.jgit.errors.IndexReadException;
 import org.eclipse.jgit.errors.LockFailedException;
 import org.eclipse.jgit.errors.UnmergedPathException;
 import org.eclipse.jgit.events.IndexChangedEvent;
@@ -418,6 +419,12 @@ else if (snapshot == null || snapshot.isModified(liveFile)) {
 					}
 				}
 			} catch (FileNotFoundException fnfe) {
+				if (liveFile.exists()) {
+					// Panic: the index file exists but we can't read it
+					throw new IndexReadException(
+							MessageFormat.format(JGitText.get().cannotReadIndex,
+									liveFile.getAbsolutePath(), fnfe));
+				}
 				// Someone must have deleted it between our exists test
 				// and actually opening the path. That's fine, its empty.
 				//
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/errors/IndexReadException.java b/org.eclipse.jgit/src/org/eclipse/jgit/errors/IndexReadException.java
new file mode 100644
index 000000000..70f650dde
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/errors/IndexReadException.java
@@ -0,0 +1,82 @@
+/*
+ * Copyright (C) 2015, Christian Halstrick <christian.halstrick@sap.com> and
+ * other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v1.0 which accompanies this
+ * distribution, is reproduced below, and is available at
+ * http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright notice, this
+ * list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from this
+ * software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.eclipse.jgit.errors;
+
+import java.io.IOException;
+
+import org.eclipse.jgit.internal.JGitText;
+
+/**
+ * Cannot read the index. This is a serious error that users need to be made
+ * aware of.
+ *
+ * @since 4.2
+ */
+public class IndexReadException extends IOException {
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * Constructs an IndexReadException with the default message.
+	 */
+	public IndexReadException() {
+		super(JGitText.get().indexWriteException);
+	}
+
+	/**
+	 * Constructs an IndexReadException with the specified detail message.
+	 *
+	 * @param s
+	 *            message
+	 */
+	public IndexReadException(final String s) {
+		super(s);
+	}
+
+	/**
+	 * Constructs an IndexReadException with the specified detail message.
+	 *
+	 * @param s
+	 *            message
+	 * @param cause
+	 *            root cause exception
+	 */
+	public IndexReadException(final String s, final Throwable cause) {
+		super(s);
+		initCause(cause);
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
index e39469bd8..be29feabd 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
@@ -146,6 +146,7 @@ public static JGitText get() {
 	/***/ public String cannotReadCommit;
 	/***/ public String cannotReadFile;
 	/***/ public String cannotReadHEAD;
+	/***/ public String cannotReadIndex;
 	/***/ public String cannotReadObject;
 	/***/ public String cannotReadObjectsPath;
 	/***/ public String cannotReadTree;