diff --git a/R/createHashFromColumns.R b/R/createHashFromColumns.R
index 1a9a799..a62572c 100644
--- a/R/createHashFromColumns.R
+++ b/R/createHashFromColumns.R
@@ -1,18 +1,26 @@
 # createHashFromColumns --------------------------------------------------------
-createHashFromColumns <- function(data, columns, n.chars = 8L)
+createHashFromColumns <- function(data, columns, nchars = 8L, silent = FALSE)
 {
   duplicates <- kwb.utils::findPartialDuplicates(data, columns)
   
   if (!is.null(duplicates)) {
-    print(duplicates)
-    stop("There are duplicates in the key columns (see above)!")
+    
+    if (!silent) {
+      message(
+        "Cannot create unique hashes due to duplicates in the key columns (",
+        kwb.utils::stringList(columns), 
+        ")! Returning -1L. Check attribute 'duplicates'."
+      )
+    }
+    
+    return(structure(-1L, duplicates = duplicates))
   }
   
   keys <- kwb.utils::pasteColumns(data, columns, "|")
   
   stopifnot(!anyDuplicated(keys))
   
-  hashes <- kwb.utils::left(unlist(lapply(keys, digest::digest)), n.chars)
+  hashes <- kwb.utils::left(unlist(lapply(keys, digest::digest)), nchars)
   
   stopifnot(!anyDuplicated(hashes))
   
diff --git a/R/setGlobalInspectionID.R b/R/setGlobalInspectionID.R
index 08c5644..dabf66b 100644
--- a/R/setGlobalInspectionID.R
+++ b/R/setGlobalInspectionID.R
@@ -12,6 +12,8 @@
 #'   seconds, just to increase the chance that setting the time is enough to
 #'   generate a unique key.
 #' @param name.convention one of \code{c("norm", "camel", "snake")}
+#' @param file optional. Path to file to which duplicates are are written (if 
+#'   any). Default: \code{"setGlobalInspectionID_duplicates.txt"}
 #' @return list with the same elements as in \code{inspection.data} but with
 #'   columns \code{inspid} being added to the data frames "inspections" and
 #'   "observations"
@@ -19,7 +21,8 @@ setGlobalInspectionID <- function(
     inspection.data, 
     project = NULL, 
     default.time = "22:22",
-    name.convention = "norm"
+    name.convention = "norm",
+    file = NULL
 )
 {
   if (is.null(project)) {
@@ -97,10 +100,16 @@ setGlobalInspectionID <- function(
   ))
   
   # Create the inspection IDs and store them in column "inspection_id"
-  inspections[["inspection_id"]] <- createHashFromColumns(
-    data = inspections,
-    columns = columns
+  hashes <- createHashFromColumns(
+    data = inspections, 
+    columns = columns, 
+    silent = TRUE
   )
+  
+  # Check for duplicates in the hashes
+  stop_on_hash_duplicates(hashes, file = file)
+
+  inspections[["inspection_id"]] <- hashes
 
   i <- kwb.utils::selectColumns(observations, "inspno")
   
@@ -111,11 +120,33 @@ setGlobalInspectionID <- function(
   observations <- kwb.utils::removeColumns(observations, "inspno")
 
   # Just a shortcut
-  idFirst <- function(df) kwb.utils::moveColumnsToFront(df, "inspection_id")
+  id_first <- function(x) kwb.utils::moveColumnsToFront(x, "inspection_id")
 
   list(
     header.info = get_elements(inspection.data, "header.info"),
-    inspections = idFirst(inspections),
-    observations = idFirst(observations)
+    inspections = id_first(inspections),
+    observations = id_first(observations)
   )
 }
+
+# stop_on_hash_duplicates ------------------------------------------------------
+stop_on_hash_duplicates <- function(hashes, file = NULL)
+{
+  if (identical(kwb.utils::removeAttributes(hashes), -1L)) {
+    
+    duplicates <- kwb.utils::getAttribute(hashes, "duplicates")
+    
+    if (is.null(file)) {
+      print(duplicates)
+    } else {
+      writeLines(capture.output(print(duplicates)), file)
+    }
+    
+    stop(
+      "There were duplicates in the key columns (see ", 
+      ifelse(is.null(file), "above", dQuote(file, '"')),
+      ").",
+      call. = FALSE
+    )
+  }
+}
diff --git a/man/setGlobalInspectionID.Rd b/man/setGlobalInspectionID.Rd
index fc68193..3691dae 100644
--- a/man/setGlobalInspectionID.Rd
+++ b/man/setGlobalInspectionID.Rd
@@ -8,7 +8,8 @@ setGlobalInspectionID(
   inspection.data,
   project = NULL,
   default.time = "22:22",
-  name.convention = "norm"
+  name.convention = "norm",
+  file = NULL
 )
 }
 \arguments{
@@ -24,6 +25,9 @@ seconds, just to increase the chance that setting the time is enough to
 generate a unique key.}
 
 \item{name.convention}{one of \code{c("norm", "camel", "snake")}}
+
+\item{file}{optional. Path to file to which duplicates are are written (if 
+any). Default: \code{"setGlobalInspectionID_duplicates.txt"}}
 }
 \value{
 list with the same elements as in \code{inspection.data} but with
diff --git a/tests/testthat/test-function-setGlobalInspectionID.R b/tests/testthat/test-function-setGlobalInspectionID.R
index 5b40ac8..8c8996c 100644
--- a/tests/testthat/test-function-setGlobalInspectionID.R
+++ b/tests/testthat/test-function-setGlobalInspectionID.R
@@ -1,7 +1,30 @@
+library(testthat)
+
 test_that("setGlobalInspectionID() works", {
 
   f <- kwb.en13508.2:::setGlobalInspectionID
 
   expect_error(f())
 
+  file <- file.path(tempdir(), "duplicates.txt")
+  
+  expect_error(f(
+    inspection.data = list(
+      inspections = data.frame(
+        inspection_date = "2024-01-03",
+        inspection_time = "22:22",
+        node_1_ref = "A",
+        node_2_ref = "B"
+      )[c(1, 1), ],
+      observations = data.frame(
+        inspno = 1L
+      ),
+      header.info = list()
+    ),
+    project = "Lausanne", 
+    name.convention = "snake",
+    file = file
+  ))
+
+  expect_true(file.exists(file))  
 })