diff --git a/metis_l2_prep_uv.pro b/metis_l2_prep_uv.pro
index 58b30a2e4f9603fe7711bbbc57f94d9e8324f051..61ad821d6763e258d7305daa277cebbdcbab5992 100644
--- a/metis_l2_prep_uv.pro
+++ b/metis_l2_prep_uv.pro
@@ -200,7 +200,7 @@ pro metis_l2_prep_uv
 	fxaddpar, extension_header, 'EXTNAME', 'Error matrix', 'Extension name'
 	error_matrix = data * sqrt(error)
 	if not ref_detector then error_matrix = metis_rectify(error_matrix, 'UV')
-	fits_add_checksum, extension_header, error_matrix
+	fits_add_checksum, extension_header, float(error_matrix)
 	mwrfits, float(error_matrix), out_file_name, extension_header, /no_comment, /silent
 
 	journal, 'Error-matrix extension correctly added.'
diff --git a/metis_l2_prep_vl_generic.pro b/metis_l2_prep_vl_generic.pro
index a0b17537ebe8ac1459812051daa1397063a3237c..0af74c20397a84e3af6727ef9b2ee31a6bd5e7db 100644
--- a/metis_l2_prep_vl_generic.pro
+++ b/metis_l2_prep_vl_generic.pro
@@ -233,7 +233,7 @@ pro metis_l2_prep_vl_generic
 	fxaddpar, extension_header, 'EXTNAME', 'Error matrix', 'Extension name'
 	error_matrix = data * sqrt(error)
 	if not ref_detector then data = metis_rectify(error_matrix, 'VL')
-	fits_add_checksum, extension_header, intarr(header.naxis1, header.naxis2)
+	fits_add_checksum, extension_header, float(error_matrix)
 	mwrfits, float(error_matrix), out_file_name, extension_header, /no_comment, /silent
 
 	journal, 'Error-matrix extension correctly added.'