diff --git a/Process.h b/Process.h
index fce5017d..e9c42622 100644
--- a/Process.h
+++ b/Process.h
@@ -76,10 +76,10 @@ typedef struct Process_ {
    pid_t tgid;
 
    /* Process group identifier */
-   unsigned int pgrp;
+   int pgrp;
 
    /* Session identifier */
-   unsigned int session;
+   int session;
 
    /* Foreground group identifier of the controlling terminal */
    int tpgid;
diff --git a/linux/LinuxProcessList.c b/linux/LinuxProcessList.c
index 5c15c2e1..081b31e0 100644
--- a/linux/LinuxProcessList.c
+++ b/linux/LinuxProcessList.c
@@ -316,11 +316,11 @@ static bool LinuxProcessList_readStatFile(Process* process, openat_arg_t procFd,
    location += 1;
 
    /* (5) pgrp  -  %d */
-   process->pgrp = strtoul(location, &location, 10);
+   process->pgrp = strtol(location, &location, 10);
    location += 1;
 
    /* (6) session  -  %d */
-   process->session = strtoul(location, &location, 10);
+   process->session = strtol(location, &location, 10);
    location += 1;
 
    /* (7) tty_nr  -  %d */