diff --git a/definitions/grib2/boot.def b/definitions/grib2/boot.def
index b92116397..c3e5d876d 100644
--- a/definitions/grib2/boot.def
+++ b/definitions/grib2/boot.def
@@ -20,6 +20,7 @@ constant grib2divider = 1000000;
 alias extraDimensionPresent = zero;
 transient angleSubdivisions = grib2divider; # micro degrees
 transient forceStepUnits = 255 : hidden;
+transient minus_one = -1: hidden;
 
 meta gts_header gts_header() : no_copy,hidden,read_only;
 meta gts_TTAAii gts_header(20,6) : no_copy,hidden,read_only;
diff --git a/definitions/grib2/parameters.def b/definitions/grib2/parameters.def
index aa2b41abe..6f4fdfccb 100644
--- a/definitions/grib2/parameters.def
+++ b/definitions/grib2/parameters.def
@@ -27,7 +27,8 @@ concept cfVarNameECMF (cfVarNameLegacyECMF,"cfVarName.def",conceptsMasterDir,con
 concept cfVarName (cfVarNameECMF,"cfVarName.def",conceptsDir2,conceptsDir1): no_copy,dump;
 
 if (tablesVersion >= 31 ) {
-  concept chemId (zero,"chemId.def",conceptsDir2,conceptsDir1): no_copy,long_type,dump;
+  # Note: 0 is a valid chemId
+  concept chemId (minus_one,"chemId.def",conceptsDir2,conceptsDir1): no_copy,long_type,dump;
   concept chemName (unknown,"chemName.def",conceptsDir2,conceptsDir1): no_copy,dump;
   concept chemShortName (unknown,"chemShortName.def",conceptsDir2,conceptsDir1): no_copy,dump;
   concept chemFormula (unknown,"chemFormula.def",conceptsDir2,conceptsDir1): no_copy,dump;
diff --git a/tests/grib2_paramid_chemid_split.sh b/tests/grib2_paramid_chemid_split.sh
index 05a1a9dd0..0732ed51e 100755
--- a/tests/grib2_paramid_chemid_split.sh
+++ b/tests/grib2_paramid_chemid_split.sh
@@ -42,7 +42,7 @@ result=$( ${tools_dir}/grib_get -f -p is_chemical $tempGribB )
 
 # Test non-chemical e.g. temperature. Now chem keys are present but unknown
 ${tools_dir}/grib_set -s tablesVersion=32,discipline=0,parameterCategory=0,parameterNumber=0 $sample  $tempGribA
-grib_check_key_equals $tempGribA "chemId,chemName,chemShortName" "0 unknown unknown"
+grib_check_key_equals $tempGribA "chemId,chemName,chemShortName" "-1 unknown unknown"
 
 
 # Clean up