diff --git a/src/ramcore/SamParser.cxx b/src/ramcore/SamParser.cxx
index f5dd07c..215c628 100644
--- a/src/ramcore/SamParser.cxx
+++ b/src/ramcore/SamParser.cxx
@@ -1,9 +1,33 @@
 #include "ramcore/SamParser.h"
-#include <cstring>
+#include <cerrno>
+#include <climits>
 #include <cstdlib>
+#include <cstring>
+#include <iostream>
 
 namespace ramcore {
 
+static bool StrictAtoi(const char* token, const char* field_name, int& result) {
+    char* end = nullptr;
+    errno = 0;
+    long val = strtol(token, &end, 10);
+
+    if (end == token || *end != '\0') {
+        std::cerr << "SamParser: invalid value '" << token
+                  << "' for field " << field_name
+                  << " (not a number)\n";
+        return false;
+    }
+    if (errno == ERANGE || val < INT_MIN || val > INT_MAX) {
+        std::cerr << "SamParser: value '" << token
+                  << "' for field " << field_name
+                  << " is out of range\n";
+        return false;
+    }
+    result = static_cast<int>(val);
+    return true;
+}
+
 void StripCRLF(char* str) {
     size_t len = strlen(str);
     while (len > 0 && (str[len-1] == '\n' || str[len-1] == '\r')) {
@@ -65,14 +89,14 @@ bool SamParser::ParseLine(char* line, SamRecord& record) {
     while (token) {
         switch (field_num) {
             case 0: record.qname = token; break;
-            case 1: record.flag = atoi(token); break;
+            case 1: if (!StrictAtoi(token, "FLAG", record.flag)) return false; break;
             case 2: record.rname = token; break;
-            case 3: record.pos = atoi(token); break;
-            case 4: record.mapq = atoi(token); break;
+            case 3: if (!StrictAtoi(token, "POS", record.pos)) return false; break;
+            case 4: if (!StrictAtoi(token, "MAPQ", record.mapq)) return false; break;
             case 5: record.cigar = token; break;
             case 6: record.rnext = token; break;
-            case 7: record.pnext = atoi(token); break;
-            case 8: record.tlen = atoi(token); break;
+            case 7: if (!StrictAtoi(token, "PNEXT", record.pnext)) return false; break;
+            case 8: if (!StrictAtoi(token, "TLEN", record.tlen)) return false; break;
             case 9: record.seq = token; break;
             case 10: 
                 StripCRLF(token);
diff --git a/test/ramcoretests.cxx b/test/ramcoretests.cxx
index 7dd8b24..fdd8269 100644
--- a/test/ramcoretests.cxx
+++ b/test/ramcoretests.cxx
@@ -462,4 +462,40 @@ TEST_F(ramcoreTest, QUALEncodingDecodingModes)
 
    std::remove(samFile);
    std::remove(ramFile);
-}
\ No newline at end of file
+}
+
+TEST_F(ramcoreTest, SamParserRejectsNonNumericFields)
+{
+   const char *badSam = "test_bad_fields.sam";
+   const char *rntupleFile = "test_bad_fields.root";
+
+   {
+      std::ofstream sam(badSam);
+      sam << "@HD\tVN:1.6\tSO:unsorted\n";
+      sam << "@SQ\tSN:chr1\tLN:10000\n";
+      // Non-numeric FLAG
+      sam << "read1\tBROKEN\tchr1\t100\t60\t50M\t*\t0\t0\t"
+          << std::string(50, 'A') << "\t*\n";
+      // Non-numeric POS
+      sam << "read2\t0\tchr1\tBAD\t60\t50M\t*\t0\t0\t"
+          << std::string(50, 'A') << "\t*\n";
+      // Trailing characters in MAPQ
+      sam << "read4\t0\tchr1\t300\t60abc\t50M\t*\t0\t0\t"
+          << std::string(50, 'A') << "\t*\n";
+      // Out-of-range POS
+      sam << "read5\t0\tchr1\t99999999999999\t60\t50M\t*\t0\t0\t"
+          << std::string(50, 'A') << "\t*\n";
+      // Valid record with negative TLEN
+      sam << "read3\t0\tchr1\t200\t60\t50M\t*\t0\t-150\t"
+          << std::string(50, 'A') << "\t*\n";
+   }
+
+   samtoramntuple(badSam, rntupleFile, false, false, false, 505, 0);
+
+   auto reader = ROOT::RNTupleReader::Open("RAM", rntupleFile);
+   EXPECT_EQ(reader->GetNEntries(), 1)
+      << "Only the valid record should be written; corrupted records must be rejected";
+
+   std::remove(badSam);
+   std::remove(rntupleFile);
+}