diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index a8207a48..8cf8ac09 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -2,3 +2,8 @@
 **Vulnerability:** Unvalidated inputs passed to `if()` statements can cause process crashes (`condition has length > 1`) or unexpected coercion vulnerabilities.
 **Learning:** In R, optional boolean parameters that default to `NULL` should be validated using explicit runtime type validation (e.g., `if (!is.null(flag) && (!is.logical(flag) || length(flag) != 1 || is.na(flag)))`).
 **Prevention:** Always implement explicit runtime type validation for optional boolean parameters.
+
+## 2024-09-19 - Fix Integer Overflow in readline validation
+**Vulnerability:** Weak numeric regex `^[0-9]+$` for `readline()` inputs intended for `as.integer()` coercion causes integer overflows. Inputs exceeding the 32-bit integer limit coerce to `NA`, potentially breaking downstream logic or causing crashes.
+**Learning:** Always use strictly bounded exact-match regex (e.g., `^[12]$`) when expecting specific small integer values from user input.
+**Prevention:** Use strictly bounded regular expressions when parsing numeric options from user interactive sessions.
diff --git a/DESCRIPTION b/DESCRIPTION
index f31d3e1a..c90753c5 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -10,7 +10,7 @@ Description: Automates fixed item parameter linking for test linking under
     the item response theory paradigm using mirt package estimates.
 License: GPL-3 | file LICENSE
 Imports: mirt, methods
-Suggests: testthat (>= 3.0.0)
+Suggests: testthat (>= 3.0.0), mockery
 Encoding: UTF-8
 Config/testthat/edition: 3
 Config/roxygen2/version: 8.0.0
diff --git a/R/aFIPC.R b/R/aFIPC.R
index 62546519..918e19b1 100644
--- a/R/aFIPC.R
+++ b/R/aFIPC.R
@@ -141,7 +141,7 @@ autoFIPC <-
       }
       for (attempt in seq_len(3)) {
         n <- readline(prompt = "Is it correct? (1: Yes 2: No) : ")
-        if (grepl("^[0-9]+$", n)) {
+        if (grepl("^[12]$", n)) {
           return(as.integer(n))
         }
       }
@@ -171,7 +171,7 @@ autoFIPC <-
               readline(
                 prompt = "Do you want to use default BILOG-MG priors for oldform Data? (1: Yes 2: No) : "
               )
-            if (grepl("^[0-9]+$", n)) {
+            if (grepl("^[12]$", n)) {
               return(as.integer(n))
             }
           }
@@ -390,7 +390,7 @@ autoFIPC <-
               readline(
                 prompt = "Do you want to use default BILOG-MG priors for newform Data? (1: Yes 2: No) : "
               )
-            if (grepl("^[0-9]+$", n)) {
+            if (grepl("^[12]$", n)) {
               return(as.integer(n))
             }
           }
diff --git a/tests/testthat/test-sentinel-validation.R b/tests/testthat/test-sentinel-validation.R
index 900f0ee3..d8fcb50b 100644
--- a/tests/testthat/test-sentinel-validation.R
+++ b/tests/testthat/test-sentinel-validation.R
@@ -1,7 +1,7 @@
 test_that("autoFIPC validates boolean flags for newformBILOGprior, oldformBILOGprior, and confirmCommonItems", {
   # newformBILOGprior
   expect_error(
-    aFIPC::autoFIPC(
+    autoFIPC(
       newformXData = data.frame(A=1),
       oldformYData = data.frame(A=2),
       newformCommonItemNames = c('A'),
@@ -13,7 +13,7 @@ test_that("autoFIPC validates boolean flags for newformBILOGprior, oldformBILOGp
 
   # oldformBILOGprior
   expect_error(
-    aFIPC::autoFIPC(
+    autoFIPC(
       newformXData = data.frame(A=1),
       oldformYData = data.frame(A=2),
       newformCommonItemNames = c('A'),
@@ -25,7 +25,7 @@ test_that("autoFIPC validates boolean flags for newformBILOGprior, oldformBILOGp
 
   # confirmCommonItems
   expect_error(
-    aFIPC::autoFIPC(
+    autoFIPC(
       newformXData = data.frame(A=1),
       oldformYData = data.frame(A=2),
       newformCommonItemNames = c('A'),
@@ -35,3 +35,19 @@ test_that("autoFIPC validates boolean flags for newformBILOGprior, oldformBILOGp
     "Security Error: confirmCommonItems must be a single non-NA logical value or NULL"
   )
 })
+
+test_that("readline validates exact 1 or 2 to avoid integer overflows", {
+  mockery::stub(autoFIPC, 'readline', mockery::mock("3", "9999999999", "abc", cycle = TRUE))
+  mockery::stub(autoFIPC, 'interactive', function() TRUE)
+
+  expect_error(
+    autoFIPC(
+      newformXData = data.frame(A=1),
+      oldformYData = data.frame(A=2),
+      newformCommonItemNames = c('A'),
+      oldformCommonItemNames = c('A'),
+      confirmCommonItems = NULL
+    ),
+    "Too many invalid common item confirmation attempts"
+  )
+})