diff --git a/src/bits_intern.h b/src/bits_intern.h
index 15963cbf3b..c4ca683ccf 100644
--- a/src/bits_intern.h
+++ b/src/bits_intern.h
@@ -13,7 +13,7 @@
 
 #include "system.h"
 
-#include <string.h>
+#include <string.h>     // for memcpy
 
 
 #define ALL_BITS_UINT  (~(UInt)0)
diff --git a/src/debug.c b/src/debug.c
index 31b0265f00..d0e981b4f3 100644
--- a/src/debug.c
+++ b/src/debug.c
@@ -30,12 +30,11 @@
 
 #include "config.h"
 
-#include <stdio.h>
-#include <stdlib.h>
-
 #if defined(HAVE_BACKTRACE) && defined(GAP_PRINT_BACKTRACE)
 #include <execinfo.h>
 #include <signal.h>
+#include <stdio.h>      // for fprintf, fileno
+#include <stdlib.h>     // for exit
 
 static void BacktraceHandler(int sig) NORETURN;
 
diff --git a/src/error.c b/src/error.c
index 2b9ff546d2..f0ecef874e 100644
--- a/src/error.c
+++ b/src/error.c
@@ -36,7 +36,7 @@
 #include "hpc/thread.h"
 #endif
 
-#include <stdio.h>
+#include <stdio.h>  // for fprintf
 
 
 static Obj ErrorInner;
diff --git a/src/funcs.c b/src/funcs.c
index e7ab735fb0..9937ad4699 100644
--- a/src/funcs.c
+++ b/src/funcs.c
@@ -37,10 +37,9 @@
 #ifdef HPCGAP
 #include "hpc/guards.h"
 #include "hpc/thread.h"
+#include <stdlib.h>     // for alloca
 #endif
 
-#include <stdlib.h>
-
 
 static ModuleStateOffset FuncsStateOffset = -1;
 
diff --git a/src/gvars.c b/src/gvars.c
index c32dfa5bb9..40ba313bcd 100644
--- a/src/gvars.c
+++ b/src/gvars.c
@@ -46,11 +46,8 @@
 #include "hpc/aobjects.h"
 #include "hpc/guards.h"
 #include "hpc/thread.h"
-#include <pthread.h>
 #endif
 
-#include <stdio.h>
-
 
 #ifdef HPCGAP
 #define USE_GVAR_BUCKETS
@@ -59,6 +56,8 @@
 
 #ifdef USE_GVAR_BUCKETS
 
+#include <stdio.h>      // for sprintf
+
 #define GVAR_BUCKETS 1024
 #define GVAR_BUCKET_SIZE 1024
 
diff --git a/src/hookintrprtr.c b/src/hookintrprtr.c
index d8ca210cbf..459777545d 100644
--- a/src/hookintrprtr.c
+++ b/src/hookintrprtr.c
@@ -21,7 +21,7 @@
 
 #include "hpc/thread.h"
 
-#include <string.h>
+#include <string.h>     // for memcpy
 
 
 // List of active hooks
diff --git a/src/hpc/aobjects.c b/src/hpc/aobjects.c
index a8cd605387..abb467c9fa 100644
--- a/src/hpc/aobjects.c
+++ b/src/hpc/aobjects.c
@@ -32,7 +32,7 @@
 #include "records.h"
 #include "stringobj.h"
 
-#include <stdlib.h>
+#include <stdlib.h>     // for labs
 
 
 static Obj TYPE_ALIST;
diff --git a/src/macfloat.c b/src/macfloat.c
index 06f6e7f51d..10696e2477 100644
--- a/src/macfloat.c
+++ b/src/macfloat.c
@@ -35,8 +35,8 @@
 
 #include "config.h"
 
-#include <stdio.h>
-#include <stdlib.h>
+#include <stdio.h>      // for snprintf
+#include <stdlib.h>     // for strtod
 
 
 #define RequireMacFloat(funcname, op) \
diff --git a/src/main.c b/src/main.c
index d07bb2558a..ec2ee41d68 100644
--- a/src/main.c
+++ b/src/main.c
@@ -20,9 +20,9 @@
 
 #include "config.h"
 
-#include <stdlib.h>
-#include <string.h>
-#include <unistd.h>
+#include <stdlib.h>     // for getenv, realpath, ...
+#include <string.h>     // for snprintf
+#include <unistd.h>     // for access, readlink, ...
 
 #if defined(__APPLE__) && defined(__MACH__)
 // Workaround: TRUE / FALSE are also defined by the macOS Mach-O headers
diff --git a/src/modules.c b/src/modules.c
index 0f56c42618..c6bb9b1742 100644
--- a/src/modules.c
+++ b/src/modules.c
@@ -44,7 +44,7 @@
 #include <dlfcn.h>
 #endif
 
-#include <stdio.h>
+#include <stdio.h>      // for fprintf, stderr
 
 
 /****************************************************************************
diff --git a/src/objects.c b/src/objects.c
index 854f3c5230..062c865469 100644
--- a/src/objects.c
+++ b/src/objects.c
@@ -32,16 +32,14 @@
 #include "hpc/guards.h"
 #include "hpc/thread.h"
 #include "hpc/traverse.h"
+#include <stdio.h>      // for sprintf
+#include <stdlib.h>     // for getenv
 #endif
 
 #if defined(USE_THREADSAFE_COPYING)
 #include "hpc/traverse.h"
 #endif
 
-#include <stdio.h>
-#include <stdlib.h>
-
-
 enum {
     MAXPRINTDEPTH = 64,
 };
diff --git a/src/opers.cc b/src/opers.cc
index 911e8a02cc..e296f6b37f 100644
--- a/src/opers.cc
+++ b/src/opers.cc
@@ -46,8 +46,6 @@ extern "C" {
 #include <pthread.h>
 #endif
 
-#include <stdio.h>
-
 #include "config.h"
 
 } // extern "C"
diff --git a/src/plist.h b/src/plist.h
index 734fc62b78..52a9b2d87f 100644
--- a/src/plist.h
+++ b/src/plist.h
@@ -28,7 +28,7 @@
 
 #include "objects.h"
 
-#include <string.h>
+#include <string.h>  // for memcpy
 
 /****************************************************************************
 **
diff --git a/src/precord.c b/src/precord.c
index 90c413b3b7..d78601e7fa 100644
--- a/src/precord.c
+++ b/src/precord.c
@@ -47,7 +47,7 @@
 #include "hpc/traverse.h"
 #endif
 
-#include <stdlib.h>
+#include <stdlib.h>     // for qsort
 
 /****************************************************************************
 **
diff --git a/src/profile.c b/src/profile.c
index e4283cc2aa..daf61a4da4 100644
--- a/src/profile.c
+++ b/src/profile.c
@@ -34,10 +34,10 @@
 
 #include "config.h"
 
-#include <stdio.h>
+#include <stdio.h>                      // for fprintf, fflush, popen, pclose, fopen, fclose
 #include <sys/time.h>                   // for gettimeofday
-#include <sys/types.h>
-#include <unistd.h>
+#include <sys/types.h>                  // for pid_t
+#include <unistd.h>                     // for getpid
 #ifdef HAVE_SYS_RESOURCE_H
 #include <sys/resource.h>               // definition of 'struct rusage'
 #endif
diff --git a/src/stringobj.h b/src/stringobj.h
index d456f8799c..9b28f61107 100644
--- a/src/stringobj.h
+++ b/src/stringobj.h
@@ -24,7 +24,7 @@
 
 #include "objects.h"
 
-#include <string.h>
+#include <string.h>     // for memcpy
 
 
 /****************************************************************************
diff --git a/src/symbols.c b/src/symbols.c
index 8c20bd6f59..b4bd76be03 100644
--- a/src/symbols.c
+++ b/src/symbols.c
@@ -20,8 +20,6 @@
 #include "hpc/thread.h"
 #endif
 
-#include <stdlib.h>
-
 
 void InitSymbolTableKernel(SymbolTable *      symtab,
                            const char *       cookieCount,
diff --git a/src/symbols.h b/src/symbols.h
index 4f738d95a7..21ba53de4f 100644
--- a/src/symbols.h
+++ b/src/symbols.h
@@ -14,7 +14,7 @@
 #include "common.h"
 
 #ifdef HPCGAP
-#include <pthread.h>
+#include <pthread.h>    // for pthread_rwlock_t
 #endif
 
 // some auxiliary typedefs for SymbolTable
diff --git a/src/sysfiles.c b/src/sysfiles.c
index 2d4794acbf..1428e193be 100644
--- a/src/sysfiles.c
+++ b/src/sysfiles.c
@@ -31,7 +31,6 @@
 #include "records.h"
 #include "stats.h"
 #include "stringobj.h"
-#include "sysenv.h"
 #include "sysopt.h"
 #include "sysstr.h"
 #include "system.h"
diff --git a/src/sysmem.c b/src/sysmem.c
index b4342bd0b4..3f5cf0d68b 100644
--- a/src/sysmem.c
+++ b/src/sysmem.c
@@ -23,12 +23,11 @@
 
 #ifdef GAP_MEM_CHECK
 #include <fcntl.h>
+#include <stdlib.h>     // for qsort
+#include <unistd.h>     // for ftruncate, getpid, unlink
 #endif
 
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <unistd.h>
+#include <stdio.h>      // for fputs
 
 #ifdef HAVE_MADVISE
 #include <sys/mman.h>
@@ -36,6 +35,9 @@
 
 #ifdef HAVE_VM_ALLOCATE
 #include <mach/mach.h>
+#elif defined(HAVE_SBRK)
+#include <string.h>     // for memset
+#include <unistd.h>     // for sbrk
 #endif
 
 
diff --git a/src/trans.cc b/src/trans.cc
index 8123923468..d8bd03a1a9 100644
--- a/src/trans.cc
+++ b/src/trans.cc
@@ -64,7 +64,7 @@ extern "C" {
 #include "plist.h"
 #include "saveload.h"
 
-#include <stdio.h>
+#include <stdio.h>      // for snprintf
 
 } // extern "C"
 
diff --git a/src/trycatch.c b/src/trycatch.c
index f0569afccc..12a68deb2e 100644
--- a/src/trycatch.c
+++ b/src/trycatch.c
@@ -13,8 +13,6 @@
 
 #include "gaputils.h"
 
-#include <stdio.h>
-
 static ThrowObserver throwObservers[16];
 
 int RegisterThrowObserver(ThrowObserver func)
diff --git a/src/vars.c b/src/vars.c
index f6df0687b8..2154fd245a 100644
--- a/src/vars.c
+++ b/src/vars.c
@@ -43,7 +43,7 @@
 #include "hpc/guards.h"
 #endif
 
-#include <stdio.h>
+#include <stdio.h>      // for snprintf
 
 
 /****************************************************************************