diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/MergerTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/MergerTest.java
index 2ae9c11a7..62495fb02 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/MergerTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/MergerTest.java
@@ -842,9 +842,9 @@ public class MergerTest extends RepositoryTestCase {
 	 * Throws an exception if reading beyond limit.
 	 */
 	static class BigReadForbiddenStream extends ObjectStream.Filter {
-		int limit;
+		long limit;
 
-		BigReadForbiddenStream(ObjectStream orig, int limit) {
+		BigReadForbiddenStream(ObjectStream orig, long limit) {
 			super(orig.getType(), orig.getSize(), orig);
 			this.limit = limit;
 		}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEntry.java b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEntry.java
index d2a59c131..d4db15ce9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEntry.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEntry.java
@@ -448,9 +448,9 @@ public class DirCacheEntry {
 	 */
 	public void setAssumeValid(boolean assume) {
 		if (assume)
-			info[infoOffset + P_FLAGS] |= ASSUME_VALID;
+			info[infoOffset + P_FLAGS] |= (byte) ASSUME_VALID;
 		else
-			info[infoOffset + P_FLAGS] &= ~ASSUME_VALID;
+			info[infoOffset + P_FLAGS] &= (byte) ~ASSUME_VALID;
 	}
 
 	/**
@@ -470,9 +470,9 @@ public class DirCacheEntry {
 	 */
 	public void setUpdateNeeded(boolean updateNeeded) {
 		if (updateNeeded)
-			inCoreFlags |= UPDATE_NEEDED;
+			inCoreFlags |= (byte) UPDATE_NEEDED;
 		else
-			inCoreFlags &= ~UPDATE_NEEDED;
+			inCoreFlags &= (byte) ~UPDATE_NEEDED;
 	}
 
 	/**
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java
index ca11fb926..f10a1d812 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java
@@ -661,7 +661,7 @@ public class DfsGarbageCollector {
 	private int objectsBefore() {
 		int cnt = 0;
 		for (DfsPackFile p : packsBefore)
-			cnt += p.getPackDescription().getObjectCount();
+			cnt += (int) p.getPackDescription().getObjectCount();
 		return cnt;
 	}
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackParser.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackParser.java
index 45e3b199f..e4c37cb4c 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackParser.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackParser.java
@@ -432,7 +432,7 @@ public class DfsPackParser extends PackParser {
 		buf[len++] = (byte) ((typeCode << 4) | (sz & 15));
 		sz >>>= 4;
 		while (sz > 0) {
-			buf[len - 1] |= 0x80;
+			buf[len - 1] |= (byte) 0x80;
 			buf[len++] = (byte) (sz & 0x7f);
 			sz >>>= 7;
 		}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectoryPackParser.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectoryPackParser.java
index ade7a8e96..7d3167356 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectoryPackParser.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectoryPackParser.java
@@ -356,7 +356,7 @@ public class ObjectDirectoryPackParser extends PackParser {
 		buf[len++] = (byte) ((typeCode << 4) | (sz & 15));
 		sz >>>= 4;
 		while (sz > 0) {
-			buf[len - 1] |= 0x80;
+			buf[len - 1] |= (byte) 0x80;
 			buf[len++] = (byte) (sz & 0x7f);
 			sz >>>= 7;
 		}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/BinaryDelta.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/BinaryDelta.java
index c7e5ad623..5f69d0a88 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/BinaryDelta.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/BinaryDelta.java
@@ -142,7 +142,7 @@ public class BinaryDelta {
 		int c, shift = 0;
 		do {
 			c = delta[deltaPtr++] & 0xff;
-			baseLen |= ((long) (c & 0x7f)) << shift;
+			baseLen |= (c & 0x7f) << shift;
 			shift += 7;
 		} while ((c & 0x80) != 0);
 		if (base.length != baseLen)
@@ -155,7 +155,7 @@ public class BinaryDelta {
 		shift = 0;
 		do {
 			c = delta[deltaPtr++] & 0xff;
-			resLen |= ((long) (c & 0x7f)) << shift;
+			resLen |= (c & 0x7f) << shift;
 			shift += 7;
 		} while ((c & 0x80) != 0);
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/IndexDiff.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/IndexDiff.java
index 42d1330af..ce1eb597f 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/IndexDiff.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/IndexDiff.java
@@ -642,11 +642,12 @@ public class IndexDiff {
 	private void addConflict(String path, int stage) {
 		StageState existingStageStates = conflicts.get(path);
 		byte stageMask = 0;
-		if (existingStageStates != null)
-			stageMask |= existingStageStates.getStageMask();
+		if (existingStageStates != null) {
+			stageMask |= (byte) existingStageStates.getStageMask();
+		}
 		// stage 1 (base) should be shifted 0 times
 		int shifts = stage - 1;
-		stageMask |= (1 << shifts);
+		stageMask |= (byte) (1 << shifts);
 		StageState stageState = StageState.fromMask(stageMask);
 		conflicts.put(path, stageState);
 	}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/FooterLine.java b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/FooterLine.java
index d6fed6670..84b6d2e48 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/FooterLine.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/FooterLine.java
@@ -95,7 +95,7 @@ public final class FooterLine {
 		for (int kPtr = 0; kPtr < len;) {
 			byte b = buffer[bPtr++];
 			if ('A' <= b && b <= 'Z')
-				b += 'a' - 'A';
+				b += (byte) ('a' - 'A');
 			if (b != kRaw[kPtr++])
 				return false;
 		}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/filter/TreeFilterMarker.java b/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/filter/TreeFilterMarker.java
index 738ccbd8b..c28f03534 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/filter/TreeFilterMarker.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/filter/TreeFilterMarker.java
@@ -113,7 +113,7 @@ public class TreeFilterMarker {
 				try {
 					boolean marked = filter.include(walk);
 					if (marked)
-						marks |= (1L << index);
+						marks |= (1 << index);
 				} catch (StopWalkException e) {
 					// Don't check tree filter anymore, it will no longer
 					// match
diff --git a/tools/BUILD b/tools/BUILD
index 20c82c570..ea2b91b02 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -58,7 +58,7 @@ java_package_configuration(
         "-Xep:MissingFail:ERROR",
         "-Xep:MissingOverride:ERROR",
         "-Xep:MutableConstantField:ERROR",
-        "-Xep:NarrowingCompoundAssignment:WARN",
+        "-Xep:NarrowingCompoundAssignment:ERROR",
         "-Xep:NonAtomicVolatileUpdate:ERROR",
         "-Xep:NonOverridingEquals:ERROR",
         "-Xep:NullableConstructor:ERROR",