diff --git a/src/expression/grib_arguments.cc b/src/expression/grib_arguments.cc
index b448f7202..96a8030ec 100644
--- a/src/expression/grib_arguments.cc
+++ b/src/expression/grib_arguments.cc
@@ -53,7 +53,7 @@ void Arguments::print(grib_handle* f) const
 
 const char* Arguments::get_name(grib_handle* h, int n) const
 {
-    Expression* e         = NULL;
+    const Expression* e = NULL;
     const Arguments* args = this;
     while (args && n-- > 0) {
         args = args->next_;
@@ -68,7 +68,6 @@ const char* Arguments::get_name(grib_handle* h, int n) const
 
 const char* Arguments::get_string(grib_handle* h, int n) const
 {
-    Expression* e         = NULL;
     const Arguments* args = this;
     int ret               = 0;
     while (args && n-- > 0) {
@@ -78,7 +77,7 @@ const char* Arguments::get_string(grib_handle* h, int n) const
     if (!args)
         return NULL;
 
-    e = args->expression_;
+    const Expression* e = args->expression_;
     return e->evaluate_string(h, NULL, NULL, &ret);
 }
 
@@ -86,7 +85,6 @@ long Arguments::get_long(grib_handle* h, int n) const
 {
     int ret               = 0;
     long lres             = 0;
-    grib_expression* e    = NULL;
     const Arguments* args = this;
     while (args && n-- > 0) {
         args = args->next_;
@@ -95,7 +93,7 @@ long Arguments::get_long(grib_handle* h, int n) const
     if (!args)
         return 0;
 
-    e   = args->expression_;
+    const grib_expression* e = args->expression_;
     ret = e->evaluate_long(h, &lres);
     (void)ret;
     return lres;
@@ -106,7 +104,6 @@ double Arguments::get_double(grib_handle* h, int n) const
     int ret     = 0;
     double dres = 0.0;
 
-    Expression* e         = NULL;
     const Arguments* args = this;
     while (args && n-- > 0) {
         args = args->next_;
@@ -115,7 +112,7 @@ double Arguments::get_double(grib_handle* h, int n) const
     if (!args)
         return 0;
 
-    e   = args->expression_;
+    const Expression* e = args->expression_;
     ret = e->evaluate_double(h, &dres);
     (void)ret;
     return dres;
diff --git a/src/expression/grib_expression_class_double.h b/src/expression/grib_expression_class_double.h
index 9657b3c26..5df2cb258 100644
--- a/src/expression/grib_expression_class_double.h
+++ b/src/expression/grib_expression_class_double.h
@@ -19,7 +19,6 @@ class Double : public Expression
 public:
     Double(grib_context*, double);
 
-    void destroy(grib_context*) override {}
     void print(grib_context*, grib_handle*, FILE*) const override;
     void add_dependency(grib_accessor*) override {}
     int native_type(grib_handle*) const override;
diff --git a/src/expression/grib_expression_class_functor.cc b/src/expression/grib_expression_class_functor.cc
index e8e9cb174..901e357a5 100644
--- a/src/expression/grib_expression_class_functor.cc
+++ b/src/expression/grib_expression_class_functor.cc
@@ -45,11 +45,14 @@ int Functor::evaluate_long(grib_handle* h, long* lres) const
     }
 
     if (STR_EQUAL(name_, "abs")) {
-        grib_expression* exp = args_ ? args_->get_expression(h, 0) : nullptr;
-        long lval = 0;
-        int ret = exp->evaluate_long(h, &lval);
-        *lres = abs(lval);
-        return ret;
+        const grib_expression* exp = args_ ? args_->get_expression(h, 0) : nullptr;
+        if (exp) {
+            long lval = 0;
+            int ret = exp->evaluate_long(h, &lval);
+            *lres = abs(lval);
+            return ret;
+        }
+        return GRIB_INVALID_ARGUMENT;
     }
 
     if (STR_EQUAL(name_, "size")) {
diff --git a/src/expression/grib_expression_class_long.cc b/src/expression/grib_expression_class_long.cc
index 7b17a2595..97e667eb8 100644
--- a/src/expression/grib_expression_class_long.cc
+++ b/src/expression/grib_expression_class_long.cc
@@ -29,11 +29,6 @@ void Long::print(grib_context* c, grib_handle* f, FILE* out) const
     fprintf(out, "long(%ld)", value_);
 }
 
-void Long::destroy(grib_context* c)
-{
-    /* grib_expression_long* e = (grib_expression_long*)g; */
-}
-
 void Long::add_dependency(grib_accessor* observer)
 {
     /* grib_expression_long* e = (grib_expression_long*)g; */
diff --git a/src/expression/grib_expression_class_long.h b/src/expression/grib_expression_class_long.h
index ed77362d1..f1a609b34 100644
--- a/src/expression/grib_expression_class_long.h
+++ b/src/expression/grib_expression_class_long.h
@@ -18,7 +18,6 @@ class Long : public Expression {
 public:
     Long(long value) : value_(value) {}
 
-    void destroy(grib_context*) override;
     void print(grib_context*, grib_handle*, FILE*) const override;
     void add_dependency(grib_accessor*) override;
     int native_type(grib_handle*) const override;
diff --git a/src/expression/grib_expression_class_true.h b/src/expression/grib_expression_class_true.h
index 7b2aab874..588dfa767 100644
--- a/src/expression/grib_expression_class_true.h
+++ b/src/expression/grib_expression_class_true.h
@@ -17,7 +17,7 @@ namespace eccodes::expression {
 class True : public Expression {
 public:
     True() = default;
-    void destroy(grib_context*) override {}
+
     void print(grib_context*, grib_handle*, FILE*) const override;
     void add_dependency(grib_accessor*) override {};
     int native_type(grib_handle*) const override;