diff --git a/examples/patbench.cc b/examples/patbench.cc
index 20de5745..7362095a 100644
--- a/examples/patbench.cc
+++ b/examples/patbench.cc
@@ -123,6 +123,7 @@
 #include <vector>
 #include <unordered_map>
 
+#include <climits>
 #include <unistd.h>
 
 // We use the BSD primitives throughout as they exist on both BSD and Linux.
@@ -657,6 +658,10 @@ int main(int argc, char **argv) {
             break;
         case 'n':
             repeatCount = atoi(optarg);
+            if (repeatCount <= 0 || repeatCount > UINT_MAX) {
+                cerr << "Invalid repeatCount." << endl;
+                exit(-1);
+            }
             break;
         default:
             usage(argv[0]);
diff --git a/examples/pcapscan.cc b/examples/pcapscan.cc
index 12b94438..913fe607 100644
--- a/examples/pcapscan.cc
+++ b/examples/pcapscan.cc
@@ -58,6 +58,7 @@
 #include <unordered_map>
 #include <vector>
 
+#include <climits>
 #include <unistd.h>
 
 // We use the BSD primitives throughout as they exist on both BSD and Linux.
@@ -489,6 +490,10 @@ int main(int argc, char **argv) {
 
     // Streaming mode scans.
     double secsStreamingScan = 0.0, secsStreamingOpenClose = 0.0;
+    if (repeatCount <= 0 || repeatCount > UINT_MAX) {
+        cerr << "Invalid repeatCount." << endl;
+        exit(-1);
+    }
     for (unsigned int i = 0; i < repeatCount; i++) {
         // Open streams.
         clock.start();
diff --git a/examples/simplegrep.c b/examples/simplegrep.c
index d6bd4b39..b2c64f31 100644
--- a/examples/simplegrep.c
+++ b/examples/simplegrep.c
@@ -57,6 +57,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 #include <hs.h>
 
@@ -152,6 +153,15 @@ int main(int argc, char *argv[]) {
     char *pattern = argv[1];
     char *inputFN = argv[2];
 
+    if (access(inputFN, F_OK) != 0) {
+        fprintf(stderr, "ERROR: file doesn't exist.\n");
+        return -1;
+    }
+    if (access(inputFN, R_OK) != 0) {
+        fprintf(stderr, "ERROR: can't be read.\n");
+        return -1;
+    }
+
     /* First, we attempt to compile the pattern provided on the command line.
      * We assume 'DOTALL' semantics, meaning that the '.' meta-character will
      * match newline characters. The compiler will analyse the given pattern and