diff --git a/src/eccodes.c b/src/eccodes.c
index 0a60f4b2e..67c4512ef 100644
--- a/src/eccodes.c
+++ b/src/eccodes.c
@@ -69,7 +69,7 @@ void codes_check(const char* call, const char* file, int line, int e, const char
 
 /* Fieldsets */
 /******************************************************************************/
-grib_fieldset* codes_fieldset_new_from_files(grib_context* c, char* filenames[], int nfiles, char** keys, int nkeys, const char* where_string, const char* order_by_string, int* err)
+grib_fieldset* codes_fieldset_new_from_files(grib_context* c, char* filenames[], int nfiles, const char** keys, int nkeys, const char* where_string, const char* order_by_string, int* err)
 {
     return grib_fieldset_new_from_files(c, filenames, nfiles, keys, nkeys, where_string, order_by_string, err);
 }
diff --git a/src/eccodes.h b/src/eccodes.h
index 932ac6cd7..2cb496176 100644
--- a/src/eccodes.h
+++ b/src/eccodes.h
@@ -181,7 +181,7 @@ typedef struct grib_util_packing_spec codes_util_packing_spec;
 typedef struct grib_util_grid_spec codes_util_grid_spec;
 
 
-codes_fieldset* codes_fieldset_new_from_files(codes_context* c, char* filenames[], int nfiles, char** keys, int nkeys, const char* where_string, const char* order_by_string, int* err);
+codes_fieldset* codes_fieldset_new_from_files(codes_context* c, char* filenames[], int nfiles, const char** keys, int nkeys, const char* where_string, const char* order_by_string, int* err);
 
 void codes_fieldset_delete(codes_fieldset* set);
 void codes_fieldset_rewind(codes_fieldset* set);
diff --git a/src/grib_api.h b/src/grib_api.h
index d8d8b3385..19b4d72b9 100644
--- a/src/grib_api.h
+++ b/src/grib_api.h
@@ -235,7 +235,7 @@ typedef struct bufr_descriptor bufr_descriptor;
 typedef struct bufr_descriptors_array bufr_descriptors_array;
 typedef struct bufr_descriptors_map_list bufr_descriptors_map_list;
 
-grib_fieldset* grib_fieldset_new_from_files(grib_context* c, char* filenames[], int nfiles, char** keys, int nkeys, const char* where_string, const char* order_by_string, int* err);
+grib_fieldset* grib_fieldset_new_from_files(grib_context* c, char* filenames[], int nfiles, const char** keys, int nkeys, const char* where_string, const char* order_by_string, int* err);
 void grib_fieldset_delete(grib_fieldset* set);
 void grib_fieldset_rewind(grib_fieldset* set);
 int grib_fieldset_apply_order_by(grib_fieldset* set, const char* order_by_string);
diff --git a/src/grib_api_prototypes.h b/src/grib_api_prototypes.h
index f0752939d..9254b9f6d 100644
--- a/src/grib_api_prototypes.h
+++ b/src/grib_api_prototypes.h
@@ -987,7 +987,7 @@ long grib_date_to_julian(long ddate);
 
 /* grib_fieldset.c */
 int grib_fieldset_new_column(grib_fieldset* set, int id, char* key, int type);
-grib_fieldset* grib_fieldset_new_from_files(grib_context* c, char* filenames[], int nfiles, char** keys, int nkeys, const char* where_string, const char* order_by_string, int* err);
+grib_fieldset* grib_fieldset_new_from_files(grib_context* c, char* filenames[], int nfiles, const char** keys, int nkeys, const char* where_string, const char* order_by_string, int* err);
 int grib_fieldset_apply_where(grib_fieldset* set, const char* where_string);
 int grib_fieldset_apply_order_by(grib_fieldset* set, const char* order_by_string);
 void grib_fieldset_delete_order_by(grib_context* c, grib_order_by* order_by);
diff --git a/src/grib_fieldset.c b/src/grib_fieldset.c
index 84b2ad400..54538b7c2 100644
--- a/src/grib_fieldset.c
+++ b/src/grib_fieldset.c
@@ -38,7 +38,7 @@ GRIB_INLINE static int grib_inline_strcmp(const char* a, const char* b)
     return (*a == 0 && *b == 0) ? 0 : 1;
 }
 
-static grib_fieldset* grib_fieldset_create_from_keys(grib_context* c, char** keys, int nkeys, int* err);
+static grib_fieldset* grib_fieldset_create_from_keys(grib_context* c, const char** keys, int nkeys, int* err);
 static grib_fieldset* grib_fieldset_create_from_order_by(grib_context* c, grib_order_by* ob,
                                                          int* err);
 static int grib_fieldset_resize(grib_fieldset* set, size_t newsize);
@@ -255,7 +255,7 @@ static int grib_fieldset_column_copy_from_handle(grib_handle* h, grib_fieldset*
 
 /* --------------- grib_fieldset functions ------------------*/
 grib_fieldset* grib_fieldset_new_from_files(grib_context* c, char* filenames[],
-                                            int nfiles, char** keys, int nkeys,
+                                            int nfiles, const char** keys, int nkeys,
                                             const char* where_string, const char* order_by_string, int* err)
 {
     int i             = 0;
@@ -316,7 +316,7 @@ grib_fieldset* grib_fieldset_new_from_files(grib_context* c, char* filenames[],
     return set;
 }
 
-static grib_fieldset* grib_fieldset_create_from_keys(grib_context* c, char** keys, int nkeys, int* err)
+static grib_fieldset* grib_fieldset_create_from_keys(grib_context* c, const char** keys, int nkeys, int* err)
 {
     grib_fieldset* set = NULL;
     size_t msize = 0, size = 0;
@@ -384,7 +384,7 @@ static grib_fieldset* grib_fieldset_create_from_keys(grib_context* c, char** key
 
 static grib_fieldset* grib_fieldset_create_from_order_by(grib_context* c, grib_order_by* ob, int* err)
 {
-    char** keys         = NULL;
+    const char** keys   = NULL;
     size_t nkeys        = 0;
     int i               = 0;
     grib_fieldset* set  = NULL;
@@ -395,7 +395,7 @@ static grib_fieldset* grib_fieldset_create_from_order_by(grib_context* c, grib_o
         next = next->next;
     }
 
-    keys = (char**)grib_context_malloc_clear(c, nkeys * sizeof(char*));
+    keys = (const char**)grib_context_malloc_clear(c, nkeys * sizeof(char*));
 
     next = ob;
     i    = 0;
diff --git a/tests/grib_fieldset.c b/tests/grib_fieldset.c
index 56e17b8ff..ff476ab45 100644
--- a/tests/grib_fieldset.c
+++ b/tests/grib_fieldset.c
@@ -25,7 +25,7 @@ int main(int argc, char** argv)
     long step;
     char** filenames;
     size_t nkeys, nfiles, i=0;
-    char* keys[] = { "step:i", "date", "paramId", "levelType" };
+    const char* keys[] = { "step:i", "date", "paramId", "levelType" };
     grib_fieldset* set = NULL;
     grib_handle* h = NULL;
     char param[20] = {0,};