diff --git a/src/DebugLogger.h b/src/DebugLogger.h
index bd61531de1..4756cba0f9 100644
--- a/src/DebugLogger.h
+++ b/src/DebugLogger.h
@@ -9,7 +9,7 @@
 
 #include "zeek/zeek-config.h"
 
-#include <stdio.h>
+#include <cstdio>
 #include <set>
 #include <string>
 
diff --git a/src/EquivClass.h b/src/EquivClass.h
index c2a3e5fad6..3e4538e769 100644
--- a/src/EquivClass.h
+++ b/src/EquivClass.h
@@ -2,7 +2,7 @@
 
 #pragma once
 
-#include <stdio.h>
+#include <cstdio>
 
 namespace zeek::detail {
 
diff --git a/src/List.h b/src/List.h
index b8351c5dc3..5a02e4879d 100644
--- a/src/List.h
+++ b/src/List.h
@@ -21,11 +21,10 @@
 //	Entries must be either a pointer to the data or nonzero data with
 //	sizeof(data) <= sizeof(void*).
 
-#include <stdarg.h>
 #include <cassert>
+#include <cstdarg>
 #include <initializer_list>
 #include <iterator>
-#include <utility>
 
 #include "zeek/util.h"
 
diff --git a/src/Reporter.h b/src/Reporter.h
index 9c03920dce..2a7d8496de 100644
--- a/src/Reporter.h
+++ b/src/Reporter.h
@@ -2,7 +2,7 @@
 
 #pragma once
 
-#include <stdarg.h>
+#include <cstdarg>
 #include <list>
 #include <map>
 #include <string>
diff --git a/src/iosource/pcap/Source.cc b/src/iosource/pcap/Source.cc
index 9bb3d7833e..b1270d9fc6 100644
--- a/src/iosource/pcap/Source.cc
+++ b/src/iosource/pcap/Source.cc
@@ -10,7 +10,7 @@
 #include <pcap-int.h>
 #endif
 
-#include <stdio.h>
+#include <cstdio>
 
 #include "zeek/Event.h"
 #include "zeek/iosource/BPF_Program.h"
diff --git a/src/re-scan.l b/src/re-scan.l
index 22d961f7f2..7fdab530fc 100644
--- a/src/re-scan.l
+++ b/src/re-scan.l
@@ -5,11 +5,11 @@
  */
 
 %top{
-// Include stdint.h at the start of the generated file. Typically
+// Include cstdint at the start of the generated file. Typically
 // MSVC will include this header later, after the definitions of
 // the integral type macros. MSVC then complains that about the
-// redefinition of the types. Including stdint.h early avoids this.
-#include <stdint.h>
+// redefinition of the types. Including cstdint early avoids this.
+#include <cstdint>
 }
 
 %{
diff --git a/src/rule-parse.y b/src/rule-parse.y
index bd11a28710..6bba57a3b3 100644
--- a/src/rule-parse.y
+++ b/src/rule-parse.y
@@ -1,6 +1,6 @@
 %{
 #include "zeek/zeek-config.h"
-#include <stdio.h>
+#include <cstdio>
 #include <netinet/in.h>
 #include <vector>
 
diff --git a/src/rule-scan.l b/src/rule-scan.l
index 04b8a3b1c6..eef1835484 100644
--- a/src/rule-scan.l
+++ b/src/rule-scan.l
@@ -1,9 +1,9 @@
 %top{
-// Include stdint.h at the start of the generated file. Typically
+// Include cstdint at the start of the generated file. Typically
 // MSVC will include this header later, after the definitions of
 // the integral type macros. MSVC then complains that about the
-// redefinition of the types. Including stdint.h early avoids this.
-#include <stdint.h>
+// redefinition of the types. Including cstdint early avoids this.
+#include <cstdint>
 }
 
 %{
diff --git a/src/scan.l b/src/scan.l
index e3bc35d379..8a5d796736 100644
--- a/src/scan.l
+++ b/src/scan.l
@@ -1,9 +1,9 @@
 %top{
-// Include stdint.h at the start of the generated file. Typically
+// Include cstdint at the start of the generated file. Typically
 // MSVC will include this header later, after the definitions of
 // the integral type macros. MSVC then complains that about the
-// redefinition of the types. Including stdint.h early avoids this.
-#include <stdint.h>
+// redefinition of the types. Including cstdint early avoids this.
+#include <cstdint>
 }
 
 %{
diff --git a/src/telemetry/ProcessStats.cc b/src/telemetry/ProcessStats.cc
index 58c534c64b..feaee81224 100644
--- a/src/telemetry/ProcessStats.cc
+++ b/src/telemetry/ProcessStats.cc
@@ -9,10 +9,10 @@
 #include <libproc.h>
 #include <mach/mach.h>
 #include <mach/task.h>
-#include <math.h>
-#include <stdlib.h>
 #include <sys/resource.h>
 #include <unistd.h>
+#include <cmath>
+#include <cstdlib>
 
 namespace zeek::telemetry::detail {
 
diff --git a/src/util.h b/src/util.h
index b5cff50e6e..677b171b66 100644
--- a/src/util.h
+++ b/src/util.h
@@ -63,8 +63,6 @@
 extern HeapLeakChecker* heap_checker;
 #endif
 
-#include <stdint.h>
-
 extern "C" {
 #include "zeek/3rdparty/modp_numtoa.h"
 }
diff --git a/src/zeekygen/Configuration.h b/src/zeekygen/Configuration.h
index 3bc5f10ee6..2256e0fde7 100644
--- a/src/zeekygen/Configuration.h
+++ b/src/zeekygen/Configuration.h
@@ -2,7 +2,7 @@
 
 #pragma once
 
-#include <time.h> // for time_t
+#include <ctime> // for time_t
 #include <string>
 #include <vector>
 
diff --git a/src/zeekygen/IdentifierInfo.h b/src/zeekygen/IdentifierInfo.h
index 346a0ab4f2..9fa9996281 100644
--- a/src/zeekygen/IdentifierInfo.h
+++ b/src/zeekygen/IdentifierInfo.h
@@ -2,7 +2,7 @@
 
 #pragma once
 
-#include <time.h> // for time_t
+#include <ctime> // for time_t
 #include <list>
 #include <map>
 #include <string>
diff --git a/src/zeekygen/PackageInfo.h b/src/zeekygen/PackageInfo.h
index 5da3df1862..574a709fe4 100644
--- a/src/zeekygen/PackageInfo.h
+++ b/src/zeekygen/PackageInfo.h
@@ -2,7 +2,7 @@
 
 #pragma once
 
-#include <time.h> // for time_t
+#include <ctime> // for time_t
 #include <string>
 #include <vector>
 
diff --git a/src/zeekygen/ScriptInfo.h b/src/zeekygen/ScriptInfo.h
index d010057f8a..bec033263d 100644
--- a/src/zeekygen/ScriptInfo.h
+++ b/src/zeekygen/ScriptInfo.h
@@ -4,7 +4,7 @@
 
 #include "zeek/zeek-config.h"
 
-#include <time.h> // for time_t
+#include <ctime> // for time_t
 #include <list>
 #include <map>
 #include <set>
diff --git a/src/zeekygen/SpicyModuleInfo.h b/src/zeekygen/SpicyModuleInfo.h
index 634d0c3228..faddc8a3ff 100644
--- a/src/zeekygen/SpicyModuleInfo.h
+++ b/src/zeekygen/SpicyModuleInfo.h
@@ -2,7 +2,7 @@
 
 #pragma once
 
-#include <time.h> // for time_t
+#include <ctime> // for time_t
 #include <list>
 #include <string>
 #include <vector>
diff --git a/src/zeekygen/utils.h b/src/zeekygen/utils.h
index c3f375990b..0537ced888 100644
--- a/src/zeekygen/utils.h
+++ b/src/zeekygen/utils.h
@@ -4,7 +4,7 @@
 
 #include "zeek/zeek-config.h"
 
-#include <time.h> // for time_t
+#include <ctime> // for time_t
 #include <optional>
 #include <string>