diff --git a/src/input_cp2k_xc.F b/src/input_cp2k_xc.F
index a4960aa419..910545240b 100644
--- a/src/input_cp2k_xc.F
+++ b/src/input_cp2k_xc.F
@@ -995,10 +995,10 @@ CONTAINS
       CALL keyword_release(keyword)
       CALL keyword_create(keyword, __LOCATION__, name="REFERENCE_FUNCTIONAL", &
                           description="Use parameters for this specific density functional. "// &
+                          "For available DFT-D4 functionals and parameters see: "// &
+                          "<https://github.com/dftd4/dftd4/blob/main/src/dftd4/param.f90>. "// &
                           "For available D3 and D3(BJ) parameters see: "// &
-                          "<https://www.chemie.uni-bonn.de/grimme/de/software/dft-d3>. "// &
-                          "For the defintion of D4 parameters see: "// &
-                          "<https://github.com/dftd4/dftd4>.", &
+                          "<https://www.chemie.uni-bonn.de/grimme/de/software/dft-d3>.", &
                           usage="REFERENCE_FUNCTIONAL <functional>", &
                           type_of_var=char_t)
       CALL section_add_keyword(subsection, keyword)
diff --git a/src/qs_dispersion_d4.F b/src/qs_dispersion_d4.F
index de0250f32f..dcf321e4f0 100644
--- a/src/qs_dispersion_d4.F
+++ b/src/qs_dispersion_d4.F
@@ -258,6 +258,9 @@ CONTAINS
 
       IF (dispersion_env%ref_functional == "none") THEN
          CALL get_rational_damping("pbe", param, s9=0.0_dp)
+         IF (.NOT. ALLOCATED(param)) THEN
+            CPABORT("D4: Failed to get rational damping parameters for default functional")
+         END IF
          SELECT TYPE (param)
          TYPE is (rational_damping_param)
             param%s6 = dispersion_env%s6
@@ -268,6 +271,9 @@ CONTAINS
          END SELECT
       ELSE
          CALL get_rational_damping(dispersion_env%ref_functional, param, s9=dispersion_env%s9)
+         IF (.NOT. ALLOCATED(param)) THEN
+            CPABORT("D4: Unknown reference functional '"//TRIM(dispersion_env%ref_functional)//"'")
+         END IF
          SELECT TYPE (param)
          TYPE is (rational_damping_param)
             dispersion_env%s6 = param%s6
diff --git a/src/qs_dispersion_utils.F b/src/qs_dispersion_utils.F
index 72c75d9108..24a1fa41fc 100644
--- a/src/qs_dispersion_utils.F
+++ b/src/qs_dispersion_utils.F
@@ -166,6 +166,7 @@ CONTAINS
             dispersion_env%s6 = 0._dp
             dispersion_env%sr6 = 0._dp
             dispersion_env%s8 = 0._dp
+            dispersion_env%s9 = 0._dp
             dispersion_env%a1 = 0._dp
             dispersion_env%a2 = 0._dp
             dispersion_env%eps_cn = 0._dp
@@ -175,7 +176,7 @@ CONTAINS
             IF (.NOT. explicit) THEN
                CALL section_vals_val_get(pp_section, "REFERENCE_FUNCTIONAL", explicit=exfun)
                IF (.NOT. exfun) THEN
-                  CPABORT("D4 vdW REFERENCE_FUNCTIONAL or D4_SCALING expected")
+                  CPABORT("Missing REFERENCE_FUNCTIONAL or D4_SCALING for D4")
                ELSE
                   CALL section_vals_val_get(vdw_section, &
                                             "PAIR_POTENTIAL%REFERENCE_FUNCTIONAL", &
@@ -190,6 +191,9 @@ CONTAINS
                dispersion_env%sr6 = 0.0_dp
                dispersion_env%ref_functional = "none"
             END IF
+            IF (TRIM(ADJUSTL(dispersion_env%ref_functional)) == "none") THEN
+               CPABORT("Missing REFERENCE_FUNCTIONAL or D4_SCALING for D4")
+            END IF
             CALL section_vals_val_get(pp_section, "EPS_CN", r_val=dispersion_env%eps_cn)
             CALL section_vals_val_get(pp_section, "D4_REFERENCE_CODE", &
                                       l_val=dispersion_env%d4_reference_code)