diff --git a/lib/base/tcpsocket.cpp b/lib/base/tcpsocket.cpp
index a9390e5a7..01594fdf3 100644
--- a/lib/base/tcpsocket.cpp
+++ b/lib/base/tcpsocket.cpp
@@ -32,8 +32,8 @@ void TcpSocket::Bind(const String& node, const String& service, int family)
 {
 	addrinfo hints;
 	addrinfo *result;
-	int error;
-	const char *func;
+	int error = 0;
+	const char *func = nullptr;
 
 	memset(&hints, 0, sizeof(hints));
 	hints.ai_family = family;
@@ -126,8 +126,8 @@ void TcpSocket::Connect(const String& node, const String& service)
 {
 	addrinfo hints;
 	addrinfo *result;
-	int error;
-	const char *func;
+	int error = 0;
+	const char *func = nullptr;
 
 	memset(&hints, 0, sizeof(hints));
 	hints.ai_family = AF_UNSPEC;
diff --git a/lib/icinga/legacytimeperiod.cpp b/lib/icinga/legacytimeperiod.cpp
index 55bc58ed3..5d2dd76b3 100644
--- a/lib/icinga/legacytimeperiod.cpp
+++ b/lib/icinga/legacytimeperiod.cpp
@@ -552,7 +552,7 @@ Dictionary::Ptr LegacyTimePeriod::FindNextSegment(const String& daydef, const St
 				ProcessTimeRanges(timeranges, &iter, segments);
 
 				Dictionary::Ptr bestSegment;
-				double bestBegin;
+				double bestBegin = 0;
 
 				ObjectLock olock(segments);
 				for (const Dictionary::Ptr& segment : segments) {
diff --git a/tools/mkclass/class_lexer.ll b/tools/mkclass/class_lexer.ll
index 217ca492c..719cc40e3 100644
--- a/tools/mkclass/class_lexer.ll
+++ b/tools/mkclass/class_lexer.ll
@@ -26,8 +26,8 @@ do {							\
 } while (0)
 
 struct lex_buf {
-	char *buf;
-	size_t size;
+	char *buf = NULL;
+	size_t size = 0;
 };
 
 static void lb_init(lex_buf *lb)