diff --git a/definitions/mars/grib.mmsf.an.def b/definitions/mars/grib.mmsf.an.def
new file mode 100644
index 000000000..0a489319c
--- /dev/null
+++ b/definitions/mars/grib.mmsf.an.def
@@ -0,0 +1,23 @@
+#no step in type an
+unalias mars.step;
+
+if (class is "od") { alias mars.system = systemNumber; }
+if (class is "me") { alias mars.system = systemNumber; }
+if (class is "en") { alias mars.system = systemNumber; }
+if (class is "c3") { alias mars.system = systemNumber; }
+if (class is "ci") { alias mars.system = systemNumber; }
+alias mars.number = perturbationNumber;
+alias mars.method = methodNumber;
+
+if (!(class is "gw")) { # ECC-1448
+    alias mars.origin = centre;
+}
+
+# See ECC-624
+if (centre == 80 && subCentre == 98 && class is "c3") {
+  constant cnmc_cmcc = 'cmcc';
+  alias mars.origin = cnmc_cmcc;
+}
+
+if (class is "ci") { unalias mars.method; }
+
diff --git a/definitions/mars/grib.oper.efi.def b/definitions/mars/grib.oper.efi.def
new file mode 100644
index 000000000..a4cef5d68
--- /dev/null
+++ b/definitions/mars/grib.oper.efi.def
@@ -0,0 +1 @@
+alias mars.step = stepRange;
diff --git a/definitions/mars/grib.oper.em.def b/definitions/mars/grib.oper.em.def
new file mode 100644
index 000000000..a4cef5d68
--- /dev/null
+++ b/definitions/mars/grib.oper.em.def
@@ -0,0 +1 @@
+alias mars.step = stepRange;
diff --git a/definitions/mars/grib.oper.es.def b/definitions/mars/grib.oper.es.def
new file mode 100644
index 000000000..a4cef5d68
--- /dev/null
+++ b/definitions/mars/grib.oper.es.def
@@ -0,0 +1 @@
+alias mars.step = stepRange;
diff --git a/definitions/mars/grib.oper.pf.def b/definitions/mars/grib.oper.pf.def
new file mode 100644
index 000000000..48f64b0d4
--- /dev/null
+++ b/definitions/mars/grib.oper.pf.def
@@ -0,0 +1,7 @@
+if (levtype is "o2d" || levtype is "o3d") {
+   alias mars.step = stepRange;
+} else {
+   alias mars.step = endStep;
+}
+
+alias mars.number = perturbationNumber;
\ No newline at end of file
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 26592f16c..0c915abeb 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -145,6 +145,7 @@ if( HAVE_BUILD_TOOLS )
         grib_ecc-1708
         grib_ecc-1691
         grib_ecc-1766
+        grib_ecc-1829
         bufr_ecc-1028
         bufr_ecc-1195
         bufr_ecc-1259
diff --git a/tests/grib_ecc-1829.sh b/tests/grib_ecc-1829.sh
new file mode 100755
index 000000000..9e075e6b8
--- /dev/null
+++ b/tests/grib_ecc-1829.sh
@@ -0,0 +1,50 @@
+#!/bin/sh
+# (C) Copyright 2005- ECMWF.
+#
+# This software is licensed under the terms of the Apache Licence Version 2.0
+# which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
+# 
+# In applying this licence, ECMWF does not waive the privileges and immunities granted to it by
+# virtue of its status as an intergovernmental organisation nor does it submit to any jurisdiction.
+#
+
+. ./include.ctest.sh
+
+REDIRECT=/dev/null
+
+# ECC-1829: Add MARS support for stream & type combinations required for AIFS ensemble
+
+label="grib_ecc-1829_test"
+temp_grib=temp.$label.grib
+mars_sample=temp.$label.mars.grib
+sample_grib2=$ECCODES_SAMPLES_PATH/GRIB2.tmpl
+
+# Setup GRIB2 message with MARS keys
+${tools_dir}/grib_set -s setLocalDefinition=1,grib2LocalSectionNumber=1 $sample_grib2 $mars_sample
+
+# Now set ensemble related keys and check number key is present
+${tools_dir}/grib_set -s stream=oper,type=pf,productDefinitionTemplateNumber=1 $mars_sample $temp_grib
+grib_check_key_exists $temp_grib mars.number
+
+# Now set keys and check stepRange is used for mars.step for o2d and o3d fields, and that number is still present
+${tools_dir}/grib_set -s stream=oper,type=pf,productDefinitionTemplateNumber=11,param=263101,typeOfLevel=oceanSurface,startStep=0,endStep=6 $mars_sample $temp_grib
+grib_check_key_exists $temp_grib mars.number
+grib_check_key_equals $temp_grib "step" "0-6"
+${tools_dir}/grib_set -s stream=oper,type=pf,productDefinitionTemplateNumber=11,param=263501,typeOfLevel=oceanModel,level=1,startStep=0,endStep=6 $mars_sample $temp_grib
+grib_check_key_exists $temp_grib mars.number
+grib_check_key_equals $temp_grib "step" "0-6"
+
+# Now set keys and check stepRange is used for type efi data (just need any template with stat proc keys)
+${tools_dir}/grib_set -s stream=oper,type=efi,productDefinitionTemplateNumber=12,startStep=0,endStep=6 $mars_sample $temp_grib
+grib_check_key_equals $temp_grib "step" "0-6"
+
+# Now set keys and check stepRange is used for type em data
+${tools_dir}/grib_set -s stream=oper,type=em,productDefinitionTemplateNumber=12,startStep=0,endStep=6 $mars_sample $temp_grib
+grib_check_key_equals $temp_grib "step" "0-6"
+
+# Now set keys and check stepRange is used for type es data
+${tools_dir}/grib_set -s stream=oper,type=es,productDefinitionTemplateNumber=12,startStep=0,endStep=6 $mars_sample $temp_grib
+grib_check_key_equals $temp_grib "step" "0-6"
+
+# Clean up
+rm -f $temp_grib $mars_sample