diff --git a/src/ICSharpCode.SharpZipLib/Zip/ZipOutputStream.cs b/src/ICSharpCode.SharpZipLib/Zip/ZipOutputStream.cs
index 1bd544c2d..dd752eb3c 100644
--- a/src/ICSharpCode.SharpZipLib/Zip/ZipOutputStream.cs
+++ b/src/ICSharpCode.SharpZipLib/Zip/ZipOutputStream.cs
@@ -262,6 +262,12 @@ public void PutNextEntry(ZipEntry entry)
 				throw new NotImplementedException("Compression method not supported");
 			}
 
+			// A password must have been set in order to add AES encrypted entries
+			if (entry.AESKeySize > 0 && string.IsNullOrEmpty(this.Password))
+			{
+				throw new InvalidOperationException("The Password property must be set before AES encrypted entries can be added");
+			}
+
 			int compressionLevel = defaultCompressionLevel;
 
 			// Clear flags that the library manages internally
diff --git a/test/ICSharpCode.SharpZipLib.Tests/Zip/StreamHandling.cs b/test/ICSharpCode.SharpZipLib.Tests/Zip/StreamHandling.cs
index cb2c72d16..60d7a5709 100644
--- a/test/ICSharpCode.SharpZipLib.Tests/Zip/StreamHandling.cs
+++ b/test/ICSharpCode.SharpZipLib.Tests/Zip/StreamHandling.cs
@@ -502,5 +502,23 @@ public void ShouldBeAbleToReadEntriesWithInvalidFileNames()
 				}
 			}
 		}
+
+		/// <summary>
+		/// Test for https://github.com/icsharpcode/SharpZipLib/issues/507
+		/// </summary>
+		[Test]
+		[Category("Zip")]
+		public void AddingAnAESEntryWithNoPasswordShouldThrow()
+		{
+			using (var memoryStream = new MemoryStream())
+			{
+				using (var outStream = new ZipOutputStream(memoryStream))
+				{
+					var newEntry = new ZipEntry("test") { AESKeySize = 256 };
+
+					Assert.Throws<InvalidOperationException>(() => outStream.PutNextEntry(newEntry));
+				}
+			}
+		}
 	}
 }