diff --git a/R/greedyMix.R b/R/greedyMix.R
index bab5649..38aeb8f 100644
--- a/R/greedyMix.R
+++ b/R/greedyMix.R
@@ -27,6 +27,9 @@ greedyMix <- function(
   inp = NULL, popnames = NULL, fixedK = FALSE, verbose = FALSE
 ) {
   # Importing and handling data ================================================
+  if (tolower(format) %in% "fasta") {
+    stop("FASTA format not yet supported on greedyMix")
+  }
   if (tolower(format) %in% "baps") {
     data <- process_BAPS_data(data, NULL)
     c <- list(
diff --git a/tests/testthat/test-greedyMix.R b/tests/testthat/test-greedyMix.R
index 7e6da02..20380af 100644
--- a/tests/testthat/test-greedyMix.R
+++ b/tests/testthat/test-greedyMix.R
@@ -57,12 +57,15 @@ test_that("Files are imported correctly", {
     )
   )
   expect_equal(length(raw_bam[[1]]), 13)
+  expect_error(
+    greedyMix(
+      data   = file.path(path_inst, "FASTA_clustering_haploid.fasta"),
+      format = "FASTA"
+    ),
+    "FASTA format not yet supported on greedyMix"
+  )
 })
 
-df_fasta <- greedyMix(
-  data   = file.path(path_inst, "FASTA_clustering_haploid.fasta"),
-  format = "FASTA"
-)
 test_that("greedyMix() works", {
   expect_error(greedyMix(file.path(path_inst, "vcf_example.vcf")))
   expect_error(greedyMix(file.path(path_inst, "bam_example.bam")))