diff --git a/src/String.h b/src/String.h
index 2dadae7..684c49c 100644
--- a/src/String.h
+++ b/src/String.h
@@ -121,18 +121,20 @@ public:
     }
     bool toInt(int& v) const
     {
+        if (mLen <= 0 || !mDat) {
+            return false;
+        }
         v = 0;
         int i = 0;
         int sign = 1;
-        if (i > 0) {
-            if (mDat[0] == '+') {
-                ++i;
-            } else if (mDat[0] == '+') {
-                sign = -1;
-                ++i;
-            } else {
-                return false;
-            }
+        if (mDat[0] == '+') {
+            ++i;
+        } else if (mDat[0] == '-') {
+            sign = -1;
+            ++i;
+        }
+        if (i >= mLen) {
+            return false;
         }
         for ( ; i < mLen; ++i) {
             if (mDat[i] >= '0' && mDat[i] <= '9') {
diff --git a/test/run.sh b/test/run.sh
index 3ff441e..7a34a92 100755
--- a/test/run.sh
+++ b/test/run.sh
@@ -149,6 +149,7 @@ TESTS=(
     "test/logunit_vsnprintf.py"
     "test/logger_thread_init.py"
     "test/logger_unbounded_logunit.py"
+    "test/string_to_int.py"
     "test/pubsub_long_name.py"
     "test/pubsub_large_message.py"
     "test/transaction_forbid.py"
diff --git a/test/string_to_int.cpp b/test/string_to_int.cpp
new file mode 100644
index 0000000..03f7388
--- /dev/null
+++ b/test/string_to_int.cpp
@@ -0,0 +1,49 @@
+/*
+ * Verify String::toInt handles signed values.
+ */
+
+#include "../src/String.h"
+
+int main() {
+    int v = 0;
+    {
+        String s("+1", 2);
+        bool ok = s.toInt(v);
+        if (!ok || v != 1) {
+            fprintf(stderr, "toInt(+1) ok=%d v=%d len=%d dat=%c%c\n",
+                    (int)ok, v, s.length(),
+                    s.data() ? s.data()[0] : '?',
+                    s.data() ? s.data()[1] : '?');
+            return 1;
+        }
+    }
+    {
+        bool ok = String("-1", 2).toInt(v);
+        if (!ok || v != -1) {
+            fprintf(stderr, "toInt(-1) ok=%d v=%d\n", (int)ok, v);
+            return 2;
+        }
+    }
+    {
+        bool ok = String("0", 1).toInt(v);
+        if (!ok || v != 0) {
+            fprintf(stderr, "toInt(0) ok=%d v=%d\n", (int)ok, v);
+            return 3;
+        }
+    }
+    {
+        bool ok = String("+", 1).toInt(v);
+        if (ok) {
+            fprintf(stderr, "toInt(+) ok=%d v=%d\n", (int)ok, v);
+            return 4;
+        }
+    }
+    {
+        bool ok = String("-", 1).toInt(v);
+        if (ok) {
+            fprintf(stderr, "toInt(-) ok=%d v=%d\n", (int)ok, v);
+            return 5;
+        }
+    }
+    return 0;
+}
diff --git a/test/string_to_int.py b/test/string_to_int.py
new file mode 100644
index 0000000..8cc8529
--- /dev/null
+++ b/test/string_to_int.py
@@ -0,0 +1,44 @@
+#!/usr/bin/env python3
+#
+# Build and run the String::toInt sign handling test.
+#
+
+import os
+import subprocess
+import tempfile
+from test_util import parse_args, exit_with_result
+
+
+def run_test(project_root):
+    src = os.path.join(project_root, "test", "string_to_int.cpp")
+    if not os.path.exists(src):
+        print("FAIL: string_to_int.cpp not found")
+        return False
+
+    with tempfile.TemporaryDirectory() as tmp:
+        exe = os.path.join(tmp, "string_to_int")
+        cmd = [
+            "g++",
+            "-std=c++11",
+            src,
+            "-o",
+            exe,
+        ]
+        try:
+            subprocess.check_call(cmd, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
+        except Exception as exc:
+            print("FAIL: compile string_to_int:", exc)
+            return False
+        try:
+            subprocess.check_call([exe], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
+        except subprocess.CalledProcessError as exc:
+            print("FAIL: string_to_int returned", exc.returncode)
+            return False
+    return True
+
+
+if __name__ == "__main__":
+    _ = parse_args("String toInt test")
+    root = os.path.abspath(os.path.join(os.path.dirname(__file__), ".."))
+    success = run_test(root)
+    exit_with_result(success, "string toInt", "string toInt")