diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index a8207a4..a25272a 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.
+
+## 2024-08-06 - Fix integer overflow coercion vulnerability in interactive inputs
+**Vulnerability:** Integer overflow coercion vulnerability where excessively large numeric strings pass unbounded regex checks (e.g., `^[0-9]+$`) but evaluate to `NA` in `as.integer()`, causing subsequent process crashes.
+**Learning:** In R scripts, when validating interactive `readline()` numeric inputs, unbounded digit classes (e.g., `^[0-9]+$`) can lead to unexpected `NA` coercion for extremely large numbers, leading to unhandled downstream exceptions.
+**Prevention:** Strictly match interactive numeric inputs against exact expected values (e.g., `^[12]$`) rather than unbounded digit classes.
diff --git a/R/aFIPC.R b/R/aFIPC.R
index 6254651..918e19b 100644
--- a/R/aFIPC.R
+++ b/R/aFIPC.R
@@ -141,7 +141,7 @@ autoFIPC <-
       }
       for (attempt in seq_len(3)) {
         n <- readline(prompt = "Is it correct? (1: Yes 2: No) : ")
-        if (grepl("^[0-9]+$", 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 900f0ee..6a32798 100644
--- a/tests/testthat/test-sentinel-validation.R
+++ b/tests/testthat/test-sentinel-validation.R
@@ -35,3 +35,34 @@ test_that("autoFIPC validates boolean flags for newformBILOGprior, oldformBILOGp
     "Security Error: confirmCommonItems must be a single non-NA logical value or NULL"
   )
 })
+
+test_that("autoFIPC properly validates interactive readline inputs to prevent integer overflow coercion", {
+  # Mock interactive() to return TRUE
+  mock_interactive <- mockery::mock(TRUE, cycle = TRUE)
+
+  # Mock readline for confirmCommonItems (reject invalid, then valid)
+  mock_readline_confirm <- mockery::mock("3", "999999999999999999999999", "1", cycle = TRUE)
+
+  # Stub both functions in the aFIPC namespace
+  mockery::stub(aFIPC::autoFIPC, 'interactive', mock_interactive)
+  mockery::stub(aFIPC::autoFIPC, 'readline', mock_readline_confirm)
+
+  # We expect an error down the line because this is a dummy data frame, but
+  # we want to ensure it passes the readline block and doesn't get stuck or crash due to coercion
+  # We'll test oldformBILOGprior similarly by passing the confirm step
+
+  mock_readline_oldform <- mockery::mock("1", "4", "99999999999999999", "2", cycle = TRUE)
+  mockery::stub(aFIPC::autoFIPC, 'readline', mock_readline_oldform)
+
+  expect_error(
+    aFIPC::autoFIPC(
+      newformXData = data.frame(A=c(1, 2, 1, 0, 1)),
+      oldformYData = data.frame(A=c(1, 0, 1, 0, 1)),
+      newformCommonItemNames = c('A'),
+      oldformCommonItemNames = c('A'),
+      confirmCommonItems = NULL,
+      itemtype = '3PL'
+    ),
+    "Initial estimation of oldFormModel completely failed"
+  )
+})