diff --git a/proc/readproc.c b/proc/readproc.c
index 6144fc02..a53f0775 100644
--- a/proc/readproc.c
+++ b/proc/readproc.c
@@ -36,6 +36,7 @@
 #include <dirent.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <limits.h>
 #ifdef WITH_SYSTEMD
 #include <systemd/sd-login.h>
 #endif
@@ -249,7 +250,8 @@ ENTER(0x220);
         // examine a field name (hash and compare)
     base:
         if(!*S) break;
-        entry = table[(GPERF_TABLE_SIZE -1) & (asso[(int)S[3]] + asso[(int)S[2]] + asso[(int)S[0]])];
+        if((!S[0] || !S[1] || !S[2] || !S[3])) break;
+        entry = table[(GPERF_TABLE_SIZE -1) & (asso[S[3]&127] + asso[S[2]&127] + asso[S[0]&127])];
         colon = strchr(S, ':');
         if(!colon) break;
         if(colon[1]!='\t') break;
@@ -385,12 +387,12 @@ ENTER(0x220);
         continue;
     case_Groups:
     {   char *nl = strchr(S, '\n');
-        int j = nl ? (nl - S) : strlen(S);
+        size_t j = nl ? (size_t)(nl - S) : strlen(S);
 
 #ifdef FALSE_THREADS
-        if (j && !IS_THREAD(P)) {
+        if (!IS_THREAD(P) && j > 0 && j < INT_MAX) {
 #else
-        if (j) {
+        if (j > 0 && j < INT_MAX) {
 #endif
             P->supgid = malloc(j+1);        // +1 in case space disappears
             if (!P->supgid)