diff --git a/src/main/java/com/mykola2312/retracker/bencode/BDict.java b/src/main/java/com/mykola2312/retracker/bencode/BDict.java
index a0b9a09..1f1d17d 100644
--- a/src/main/java/com/mykola2312/retracker/bencode/BDict.java
+++ b/src/main/java/com/mykola2312/retracker/bencode/BDict.java
@@ -1,5 +1,6 @@
 package com.mykola2312.retracker.bencode;
 
+import com.mykola2312.retracker.bencode.error.BErrorInvalidKey;
 import com.mykola2312.retracker.bencode.error.BErrorKeyNotFound;
 import com.mykola2312.retracker.bencode.error.BErrorNoChildren;
 import com.mykola2312.retracker.bencode.error.BErrorValueCast;
@@ -11,7 +12,20 @@ public class BDict extends BList {
 		return BType.DICT;
 	}
 	
-	public BDict set(BValue key, BValue value) {
+	public BDict set(BValue key, BValue value) throws BErrorInvalidKey {
+		if (key == null || value == null) {
+			throw new BErrorInvalidKey(this, key, "key or value is null");
+		}
+		/* key type cannot have child, because it messes up tree,
+		 * in other words, key cannot be a list or dict
+		 */
+		if (key.getChild() != null) {
+			throw new BErrorInvalidKey(this, key, "key has child, because its list or a dict");
+		}
+		if (key.getType().equals(BType.LIST) || key.getType().equals(BType.DICT)) {
+			throw new BErrorInvalidKey(this, key, "key shall not be list or a dict");
+		}
+		
 		BValue node = find(key);
 		if (node != null) {
 			node.setNext(value);
@@ -24,7 +38,14 @@ public class BDict extends BList {
 	}
 	
 	public BDict set(String key, BValue value) {
-		return set(new BString(key), value);
+		/* we "suppress" here exceptions since this method is used
+		 * for building BTrees, not when decoding
+		 */
+		try {
+			return set(new BString(key), value);
+		} catch (BErrorInvalidKey e) {
+			throw new RuntimeException("this shouldn't have happened in BDict set: " + e.getMessage());
+		}
 	}
 	
 	/* since we're going to employ builder pattern, we can't return null.
diff --git a/src/main/java/com/mykola2312/retracker/bencode/BTree.java b/src/main/java/com/mykola2312/retracker/bencode/BTree.java
index 7f46e69..0e8337b 100644
--- a/src/main/java/com/mykola2312/retracker/bencode/BTree.java
+++ b/src/main/java/com/mykola2312/retracker/bencode/BTree.java
@@ -1,12 +1,14 @@
 package com.mykola2312.retracker.bencode;
 
 import static io.netty.buffer.Unpooled.buffer;
+
 import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 
 import com.mykola2312.retracker.bencode.error.BDecodeError;
 import com.mykola2312.retracker.bencode.error.BDecodeMalformed;
 import com.mykola2312.retracker.bencode.error.BDecodeParseError;
+import com.mykola2312.retracker.bencode.error.BErrorInvalidKey;
 import com.mykola2312.retracker.bencode.error.BErrorNoRoot;
 import com.mykola2312.retracker.bencode.error.BErrorValueCast;
 
@@ -102,7 +104,11 @@ public class BTree {
 				while (offset < data.length && data[offset] != BTree.BE_END) {
 					BValue key = decode();
 					BValue value = decode();
-					dict.set(key, value);
+					try {
+						dict.set(key, value);
+					} catch (BErrorInvalidKey e) {
+						throw new BDecodeMalformed(data, offset, e.getMessage());
+					}
 				}
 				// advance past terminator
 				offset++;
@@ -171,6 +177,7 @@ public class BTree {
 			case LIST:
 				buffer.writeByte(BE_LIST);
 				for (BValue item : node) {
+					System.err.println("encoding list item: " + item);
 					encode(item);
 				}
 				buffer.writeByte(BE_END);
diff --git a/src/main/java/com/mykola2312/retracker/bencode/error/BErrorInvalidKey.java b/src/main/java/com/mykola2312/retracker/bencode/error/BErrorInvalidKey.java
new file mode 100644
index 0000000..102b3c1
--- /dev/null
+++ b/src/main/java/com/mykola2312/retracker/bencode/error/BErrorInvalidKey.java
@@ -0,0 +1,11 @@
+package com.mykola2312.retracker.bencode.error;
+
+import com.mykola2312.retracker.bencode.BValue;
+
+public class BErrorInvalidKey extends BValueError {
+	private static final long serialVersionUID = 8821935501326704941L;
+
+	public BErrorInvalidKey(BValue node, BValue key, String message) {
+		super(node, String.format("key \"%s\" invalid: %s", key, message));
+	}
+}
diff --git a/src/test/java/com/mykola2312/retracker/bencode/BDictTest.java b/src/test/java/com/mykola2312/retracker/bencode/BDictTest.java
index 7898faa..4773807 100644
--- a/src/test/java/com/mykola2312/retracker/bencode/BDictTest.java
+++ b/src/test/java/com/mykola2312/retracker/bencode/BDictTest.java
@@ -8,6 +8,7 @@ import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 
 import org.junit.jupiter.api.Test;
 
+import com.mykola2312.retracker.bencode.error.BErrorInvalidKey;
 import com.mykola2312.retracker.bencode.error.BErrorKeyNotFound;
 import com.mykola2312.retracker.bencode.error.BErrorValueCast;
 import com.mykola2312.retracker.bencode.error.BValueError;
@@ -37,7 +38,7 @@ public class BDictTest {
 	}
 	
 	@Test
-	public void testKeyChild() {
+	public void testKeyChild() throws BErrorInvalidKey {
 		BDict dict = new BDict();
 		dict.set(new BInteger(1), new BInteger(2));
 		
diff --git a/src/test/java/com/mykola2312/retracker/bencode/BTreeTest.java b/src/test/java/com/mykola2312/retracker/bencode/BTreeTest.java
index fea0e54..f63333b 100644
--- a/src/test/java/com/mykola2312/retracker/bencode/BTreeTest.java
+++ b/src/test/java/com/mykola2312/retracker/bencode/BTreeTest.java
@@ -7,6 +7,7 @@ import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import java.io.IOException;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 
@@ -15,6 +16,7 @@ import org.junit.jupiter.api.Test;
 import com.mykola2312.retracker.bencode.error.BDecodeError;
 import com.mykola2312.retracker.bencode.error.BDecodeMalformed;
 import com.mykola2312.retracker.bencode.error.BError;
+import com.mykola2312.retracker.bencode.error.BErrorInvalidKey;
 
 public class BTreeTest {
 	@Test
@@ -141,6 +143,17 @@ public class BTreeTest {
 		});
 	}
 	
+	@Test
+	public void testInvalidKeys() {
+		assertThrows(BErrorInvalidKey.class, () -> {
+			new BTree().setRoot(new BDict()).set(new BList(), new BList());
+		});
+		
+		assertThrows(BDecodeMalformed.class, () -> {
+			new BTree().decode("dlelee".getBytes());
+		});
+	}
+	
 	@Test
 	public void testEncode() {
 		assertDoesNotThrow(() -> {
@@ -148,6 +161,9 @@ public class BTreeTest {
 			
 			tree.setRoot(new BInteger(1));
 			assertArrayEquals("i1e".getBytes(), tree.encode());
+			
+			tree.setRoot(new BString("test"));
+			assertArrayEquals("4:test".getBytes(), tree.encode());
 		});
 	}