diff --git a/src/ZNCDebug.cpp b/src/ZNCDebug.cpp
index 9b798454..5e2d1521 100644
--- a/src/ZNCDebug.cpp
+++ b/src/ZNCDebug.cpp
@@ -29,11 +29,16 @@ CString CDebug::Filter(const CString& sUnfilteredLine) {
 
     // If the line is a PASS command to authenticate to a server / znc
     if (sUnfilteredLine.StartsWith("PASS ")) {
+        CString sPrefix = sUnfilteredLine.substr(0, sUnfilteredLine[5] == ':' ? 6 : 5);
+        CString sRest = sUnfilteredLine.substr(sPrefix.length());
+
         VCString vsSafeCopy;
-        sUnfilteredLine.Split(":", vsSafeCopy);
+        sRest.Split(":", vsSafeCopy);
 
         if (vsSafeCopy.size() > 1) {
-            sFilteredLine = vsSafeCopy[0] + ":<censored>";
+            sFilteredLine = sPrefix + vsSafeCopy[0] + ":<censored>";
+        } else {
+            sFilteredLine = sPrefix + "<censored>";
         }
     }
 
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 2710c742..4b074563 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -61,7 +61,7 @@ add_executable(unittest_bin EXCLUDE_FROM_ALL
 	"ThreadTest.cpp" "NickTest.cpp" "ClientTest.cpp" "NetworkTest.cpp"
 	"MessageTest.cpp" "ModulesTest.cpp" "IRCSockTest.cpp" "QueryTest.cpp"
 	"StringTest.cpp" "ConfigTest.cpp" "BufferTest.cpp" "UtilsTest.cpp"
-	"UserTest.cpp")
+	"UserTest.cpp" "DebugTest.cpp")
 target_link_libraries(unittest_bin PRIVATE znclib)
 target_include_directories(unittest_bin PRIVATE
 	"${GTEST_ROOT}" "${GTEST_ROOT}/include"
diff --git a/test/DebugTest.cpp b/test/DebugTest.cpp
new file mode 100644
index 00000000..d335d811
--- /dev/null
+++ b/test/DebugTest.cpp
@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) 2004-2021 ZNC, see the NOTICE file for details.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+#include <gmock/gmock.h>
+#include <znc/ZNCDebug.h>
+
+TEST(DebugTest, Filter) {
+    EXPECT_EQ(CDebug::Filter("JOIN #znc"), "JOIN #znc");
+    EXPECT_EQ(CDebug::Filter("PASS hunter2"), "PASS <censored>");
+    EXPECT_EQ(CDebug::Filter("PASS :hunter2"), "PASS :<censored>");
+    EXPECT_EQ(CDebug::Filter("PASS user/net:hunter2"), "PASS user/net:<censored>");
+    EXPECT_EQ(CDebug::Filter("PASS :user/net:hunter2"), "PASS :user/net:<censored>");
+    EXPECT_EQ(CDebug::Filter("pass hunter2"), "pass <censored>");
+}