diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index a8207a48..0cccc72f 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.
+
+## 2024-08-27 - Fix unhandled NA coercion crash in interactive prompts
+**Vulnerability:** Weak regex `^[0-9]+$` on interactive integer inputs allows large numbers which coerce to `NA` via `as.integer()`, breaking `if` conditions and causing unhandled exceptions.
+**Learning:** Using overly permissive regex for bounded integer choices exposes the application to coercion crashes.
+**Prevention:** Use strictly bounded exact-match regex like `^[12]$` when reading integer choices via `readline()` in R to prevent coercion crashes.
diff --git a/DESCRIPTION b/DESCRIPTION
index f31d3e1a..f5216ca5 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -10,7 +10,8 @@ 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-readline-coercion.R b/tests/testthat/test-readline-coercion.R
new file mode 100644
index 00000000..c8486e17
--- /dev/null
+++ b/tests/testthat/test-readline-coercion.R
@@ -0,0 +1,16 @@
+test_that("interactive prompt handles large numbers correctly without crashing", {
+  # We mock readline to return a huge number that coerces to NA
+  my_readline <- function(...) "9999999999999999999999999"
+  mockery::stub(aFIPC::autoFIPC, 'readline', my_readline)
+  mockery::stub(aFIPC::autoFIPC, 'interactive', TRUE)
+
+  expect_error(
+    aFIPC::autoFIPC(
+      newformXData = data.frame(A=1),
+      oldformYData = data.frame(A=2),
+      newformCommonItemNames = c('A'),
+      oldformCommonItemNames = c('A')
+    ),
+    "Too many invalid common item confirmation attempts"
+  )
+})