diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsFsckTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsFsckTest.java
index 804d744ae..c1811251c 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsFsckTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsFsckTest.java
@@ -266,4 +266,59 @@ public class DfsFsckTest {
 				"refs/heads/master");
 	}
 
+	private ObjectId insertGitModules(String contents) throws IOException {
+		ObjectId blobId = ins.insert(Constants.OBJ_BLOB,
+				Constants.encode(contents));
+
+		byte[] blobIdBytes = new byte[OBJECT_ID_LENGTH];
+		blobId.copyRawTo(blobIdBytes, 0);
+		byte[] data = concat(encodeASCII("100644 .gitmodules\0"), blobIdBytes);
+		ins.insert(Constants.OBJ_TREE, data);
+		ins.flush();
+
+		return blobId;
+	}
+
+	@Test
+	public void testInvalidGitModules() throws Exception {
+		String fakeGitmodules = new StringBuilder()
+				.append("[submodule \"test\"]\n")
+				.append("    path = xlib\n")
+				.append("    url = https://example.com/repo/xlib.git\n\n")
+				.append("[submodule \"test2\"]\n")
+				.append("    path = zlib\n")
+				.append("    url = -upayload.sh\n")
+				.toString();
+
+		ObjectId blobId = insertGitModules(fakeGitmodules);
+
+		DfsFsck fsck = new DfsFsck(repo);
+		FsckError errors = fsck.check(null);
+		assertEquals(errors.getCorruptObjects().size(), 1);
+
+		CorruptObject error = errors.getCorruptObjects().iterator().next();
+		assertEquals(error.getId(), blobId);
+		assertEquals(error.getType(), Constants.OBJ_BLOB);
+		assertEquals(error.getErrorType(), ErrorType.GITMODULES_URL);
+	}
+
+
+	@Test
+	public void testValidGitModules() throws Exception {
+		String fakeGitmodules = new StringBuilder()
+				.append("[submodule \"test\"]\n")
+				.append("    path = xlib\n")
+				.append("    url = https://example.com/repo/xlib.git\n\n")
+				.append("[submodule \"test2\"]\n")
+				.append("    path = zlib\n")
+				.append("    url = ok/path\n")
+				.toString();
+
+		insertGitModules(fakeGitmodules);
+
+		DfsFsck fsck = new DfsFsck(repo);
+		FsckError errors = fsck.check(null);
+		assertEquals(errors.getCorruptObjects().size(), 0);
+	}
+
 }
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 3f1d21289..40915b7b1 100644
--- a/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
+++ b/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
@@ -769,6 +769,7 @@ uriNotFound={0} not found
 uriNotFoundWithMessage={0} not found: {1}
 URINotSupported=URI not supported: {0}
 userConfigFileInvalid=User config file {0} invalid {1}
+validatingGitModules=Validating .gitmodules files
 walkFailure=Walk failure.
 wantNotValid=want {0} not valid
 weeksAgo={0} weeks ago
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 c11ae5a52..7a9d523de 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
@@ -830,6 +830,7 @@ public class JGitText extends TranslationBundle {
 	/***/ public String uriNotFoundWithMessage;
 	/***/ public String URINotSupported;
 	/***/ public String userConfigFileInvalid;
+	/***/ public String validatingGitModules;
 	/***/ public String walkFailure;
 	/***/ public String wantNotValid;
 	/***/ public String weeksAgo;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsFsck.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsFsck.java
index 3f96d0919..c0e24c02c 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsFsck.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsFsck.java
@@ -43,6 +43,7 @@
 
 package org.eclipse.jgit.internal.storage.dfs;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.eclipse.jgit.internal.storage.pack.PackExt.INDEX;
 import static org.eclipse.jgit.internal.storage.pack.PackExt.PACK;
 
@@ -54,12 +55,18 @@ import org.eclipse.jgit.errors.MissingObjectException;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.internal.fsck.FsckError;
 import org.eclipse.jgit.internal.fsck.FsckError.CorruptIndex;
+import org.eclipse.jgit.internal.fsck.FsckError.CorruptObject;
 import org.eclipse.jgit.internal.fsck.FsckPackParser;
 import org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource;
+import org.eclipse.jgit.internal.submodule.SubmoduleValidator;
+import org.eclipse.jgit.internal.submodule.SubmoduleValidator.SubmoduleValidationException;
+import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.GitmoduleEntry;
 import org.eclipse.jgit.lib.NullProgressMonitor;
 import org.eclipse.jgit.lib.ObjectChecker;
 import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectLoader;
 import org.eclipse.jgit.lib.ProgressMonitor;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.revwalk.ObjectWalk;
@@ -102,6 +109,7 @@ public class DfsFsck {
 
 		FsckError errors = new FsckError();
 		if (!connectivityOnly) {
+			objChecker.reset();
 			checkPacks(pm, errors);
 		}
 		checkConnectivity(pm, errors);
@@ -128,6 +136,8 @@ public class DfsFsck {
 				}
 			}
 		}
+
+		checkGitModules(pm, errors);
 	}
 
 	private void verifyPack(ProgressMonitor pm, FsckError errors, DfsReader ctx,
@@ -142,6 +152,28 @@ public class DfsFsck {
 		fpp.verifyIndex(pack.getPackIndex(ctx));
 	}
 
+	private void checkGitModules(ProgressMonitor pm, FsckError errors)
+			throws IOException {
+		pm.beginTask(JGitText.get().validatingGitModules,
+				objChecker.getGitsubmodules().size());
+		for (GitmoduleEntry entry : objChecker.getGitsubmodules()) {
+			AnyObjectId blobId = entry.getBlobId();
+			ObjectLoader blob = objdb.open(blobId, Constants.OBJ_BLOB);
+
+			try {
+				SubmoduleValidator.assertValidGitModulesFile(
+						new String(blob.getBytes(), UTF_8));
+			} catch (SubmoduleValidationException e) {
+				CorruptObject co = new FsckError.CorruptObject(
+						blobId.toObjectId(), Constants.OBJ_BLOB,
+						e.getFsckMessageId());
+				errors.getCorruptObjects().add(co);
+			}
+			pm.update(1);
+		}
+		pm.endTask();
+	}
+
 	private void checkConnectivity(ProgressMonitor pm, FsckError errors)
 			throws IOException {
 		pm.beginTask(JGitText.get().countingObjects, ProgressMonitor.UNKNOWN);
@@ -179,6 +211,9 @@ public class DfsFsck {
 	 * Use a customized object checker instead of the default one. Caller can
 	 * specify a skip list to ignore some errors.
 	 *
+	 * It will be reset at the start of each {{@link #check(ProgressMonitor)}
+	 * call.
+	 *
 	 * @param objChecker
 	 *            A customized object checker.
 	 */
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectChecker.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectChecker.java
index 825f81e69..d942d6906 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectChecker.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectChecker.java
@@ -109,7 +109,8 @@ import org.eclipse.jgit.util.StringUtils;
  * the caller can provide both of these validations on its own.
  * <p>
  * Instances of this class are not thread safe, but they may be reused to
- * perform multiple object validations.
+ * perform multiple object validations, calling {@link #reset()} between them to
+ * clear the internal state (e.g. {@link #getGitsubmodules()})
  */
 public class ObjectChecker {
 	/** Header "tree " */
@@ -1258,4 +1259,19 @@ public class ObjectChecker {
 	public List<GitmoduleEntry> getGitsubmodules() {
 		return gitsubmodules;
 	}
+
+	/**
+	 * Reset the invocation-specific state from this instance. Specifically this
+	 * clears the list of .gitmodules files encountered (see
+	 * {@link #getGitsubmodules()})
+	 *
+	 * Configurations like errors to filter, skip lists or the specified O.S.
+	 * (set via {@link #setSafeForMacOS(boolean)} or
+	 * {@link #setSafeForWindows(boolean)}) are NOT cleared.
+	 *
+	 * @since 5.2
+	 */
+	public void reset() {
+		gitsubmodules.clear();
+	}
 }