diff --git a/DESCRIPTION b/DESCRIPTION
index 7e07728..11b74e6 100755
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,8 +1,8 @@
 Package: PKPDmap
 Type: Package
 Title: MAP Bayesian estimates
-Version: 1.1.4
-Date: 2025-07-12
+Version: 1.1.6
+Date: 2025-09-10
 Author: Ron Keizer, Jasmine Hughes, Kara Woo
 Maintainer: Ron Keizer <ron@insight-rx.com>
 Description: Obtain MAP Bayesian estimates based on individual data and
diff --git a/R/parse_input_data.R b/R/parse_input_data.R
index aefe23b..84bffb5 100644
--- a/R/parse_input_data.R
+++ b/R/parse_input_data.R
@@ -13,6 +13,7 @@ parse_input_data <- function(
   } else {
     data$obs_type <- data[[obs_type_label]]
   }
+  data$OBS_TYPE <- NULL # ensure there is no duplicate `obs_type` column
   colnames(data) <- tolower(colnames(data))
   if(!all(tolower(unlist(cols)) %in% names(data))) {
     stop("Expected column names were not found in data. Please use 'cols' argument to specify column names for independent and dependent variable.")
diff --git a/tests/testthat/test-parse_input_data.R b/tests/testthat/test-parse_input_data.R
index 05b279e..53df283 100644
--- a/tests/testthat/test-parse_input_data.R
+++ b/tests/testthat/test-parse_input_data.R
@@ -1,4 +1,4 @@
-test_that("parse_input_data handles regular data frame input", {
+test_that("parse_input_data handles regular data frame input, with OBS_TYPE label but not specified as `obs_type_label`", {
   # Create test data
   data <- data.frame(
     T = c(2, 1, 3),
@@ -6,16 +6,49 @@ test_that("parse_input_data handles regular data frame input", {
     Y = c(10, 20, 30)
   )
   
-  result <- parse_input_data(data)
+  result <- parse_input_data(data, obs_type_label = NULL)
   
   # Check column names are lowercase
-  expect_equal(names(result), c("t", "obs_type", "y", "obs_type"))
+  expect_equal(names(result), c("t", "y", "obs_type"))
+  
+  # Check sorting
+  expect_equal(result$t, c(1, 2, 3))
+  expect_equal(result$obs_type, c(1, 1, 1))
+
+})
+
+test_that("parse_input_data picks right column, even with lower/uppercase duplicates", {
+  data <- data.frame(
+    T = c(1, 2, 3),
+    obs_type = c(1, 0, 1),
+    OBS_TYPE = c(2, 1, 1),
+    Y = c(10, 20, 30)
+  )
+  result <- parse_input_data(data, obs_type_label = "OBS_TYPE")
+  expect_equal(result$obs_type, c(2, 1, 1))
+  expect_equal(sum(tolower(names(result)) == "obs_type"), 1)
+})
+
+test_that("parse_input_data handles regular data frame input, with OBS_TYPE label, properly specified as `obs_type_label`", {
+  # Create test data
+  data <- data.frame(
+    T = c(2, 1, 3),
+    OBS_TYPE = c(2, 1, 1),
+    Y = c(10, 20, 30)
+  )
+  
+  result <- parse_input_data(data, obs_type_label = "OBS_TYPE")
+  
+  # Check column names are lowercase
+  expect_equal(names(result), c("t", "y", "obs_type"))
   
   # Check sorting
   expect_equal(result$t, c(1, 2, 3))
   expect_equal(result$obs_type, c(1, 2, 1))
+  
 })
 
+
 test_that("parse_input_data handles PKPDsim object", {
   # Create mock PKPDsim object
   data <- structure(