diff --git a/module/Decision/src/Model/SubDecision.php b/module/Decision/src/Model/SubDecision.php
index 6bb8af9b8a..a8ab2db901 100644
--- a/module/Decision/src/Model/SubDecision.php
+++ b/module/Decision/src/Model/SubDecision.php
@@ -136,6 +136,20 @@ enumType: MeetingTypes::class,
     #[Column(type: 'text')]
     protected string $content;
 
+    /**
+     * The member involved in this sub-decision.
+     *
+     * Not all sub-decisions require this, as such it is nullable. However, sub-decisions that need the guarantee that
+     * this is not null or need to specify an inverse side can do so using an association override.
+     */
+    #[ManyToOne(targetEntity: Member::class)]
+    #[JoinColumn(
+        name: 'lidnr',
+        referencedColumnName: 'lidnr',
+        nullable: true,
+    )]
+    protected ?Member $member = null;
+
     /**
      * Get the decision.
      */
@@ -205,6 +219,22 @@ public function setNumber(int $number): void
         $this->number = $number;
     }
 
+    /**
+     * Get the member.
+     */
+    public function getMember(): ?Member
+    {
+        return $this->member;
+    }
+
+    /**
+     * Set the member.
+     */
+    public function setMember(Member $member): void
+    {
+        $this->member = $member;
+    }
+
     /**
      * Get the content.
      */
diff --git a/module/Decision/src/Model/SubDecision/Board/Installation.php b/module/Decision/src/Model/SubDecision/Board/Installation.php
index 349cf0d6cc..47de57f196 100644
--- a/module/Decision/src/Model/SubDecision/Board/Installation.php
+++ b/module/Decision/src/Model/SubDecision/Board/Installation.php
@@ -8,16 +8,27 @@
 use Decision\Model\BoardMember;
 use Decision\Model\Member;
 use Decision\Model\SubDecision;
+use Doctrine\ORM\Mapping\AssociationOverride;
+use Doctrine\ORM\Mapping\AssociationOverrides;
 use Doctrine\ORM\Mapping\Column;
 use Doctrine\ORM\Mapping\Entity;
 use Doctrine\ORM\Mapping\JoinColumn;
-use Doctrine\ORM\Mapping\ManyToOne;
 use Doctrine\ORM\Mapping\OneToOne;
 
 /**
  * Installation as board member.
  */
 #[Entity]
+#[AssociationOverrides([
+    new AssociationOverride(
+        name: 'member',
+        joinColumns: new JoinColumn(
+            name: 'lidnr',
+            referencedColumnName: 'lidnr',
+            nullable: false,
+        ),
+    ),
+])]
 class Installation extends SubDecision
 {
     /**
@@ -26,21 +37,6 @@ class Installation extends SubDecision
     #[Column(type: 'string')]
     protected string $function;
 
-    /**
-     * Member.
-     *
-     * Note that only members that are older than 18 years can be board members.
-     * Also, honorary, external and extraordinary members cannot be board members.
-     * (See the Statuten, Art. 13 Lid 2.
-     */
-    // TODO: Inversed relation
-    #[ManyToOne(targetEntity: Member::class)]
-    #[JoinColumn(
-        name: 'lidnr',
-        referencedColumnName: 'lidnr',
-    )]
-    protected Member $member;
-
     /**
      * The date at which the installation is in effect.
      */
@@ -92,20 +88,14 @@ public function setFunction(string $function): void
 
     /**
      * Get the member.
+     *
+     * @psalm-suppress InvalidNullableReturnType
      */
     public function getMember(): Member
     {
         return $this->member;
     }
 
-    /**
-     * Set the member.
-     */
-    public function setMember(Member $member): void
-    {
-        $this->member = $member;
-    }
-
     /**
      * Get the date.
      */
diff --git a/module/Decision/src/Model/SubDecision/Budget.php b/module/Decision/src/Model/SubDecision/Budget.php
index 173b5b51f2..9d33bd7814 100644
--- a/module/Decision/src/Model/SubDecision/Budget.php
+++ b/module/Decision/src/Model/SubDecision/Budget.php
@@ -5,12 +5,9 @@
 namespace Decision\Model\SubDecision;
 
 use DateTime;
-use Decision\Model\Member;
 use Decision\Model\SubDecision;
 use Doctrine\ORM\Mapping\Column;
 use Doctrine\ORM\Mapping\Entity;
-use Doctrine\ORM\Mapping\JoinColumn;
-use Doctrine\ORM\Mapping\ManyToOne;
 
 /**
  * Budget decision.
@@ -18,16 +15,6 @@
 #[Entity]
 class Budget extends SubDecision
 {
-    /**
-     * Budget author.
-     */
-    #[ManyToOne(targetEntity: Member::class)]
-    #[JoinColumn(
-        name: 'lidnr',
-        referencedColumnName: 'lidnr',
-    )]
-    protected Member $author;
-
     /**
      * Name of the budget.
      */
@@ -61,22 +48,6 @@ class Budget extends SubDecision
     #[Column(type: 'boolean')]
     protected bool $changes;
 
-    /**
-     * Get the author.
-     */
-    public function getAuthor(): Member
-    {
-        return $this->author;
-    }
-
-    /**
-     * Set the author.
-     */
-    public function setAuthor(Member $author): void
-    {
-        $this->author = $author;
-    }
-
     /**
      * Get the name.
      */
diff --git a/module/Decision/src/Model/SubDecision/Installation.php b/module/Decision/src/Model/SubDecision/Installation.php
index 522b6b52c3..1affcdcdc3 100644
--- a/module/Decision/src/Model/SubDecision/Installation.php
+++ b/module/Decision/src/Model/SubDecision/Installation.php
@@ -8,10 +8,11 @@
 use Decision\Model\OrganMember;
 use Doctrine\Common\Collections\ArrayCollection;
 use Doctrine\Common\Collections\Collection;
+use Doctrine\ORM\Mapping\AssociationOverride;
+use Doctrine\ORM\Mapping\AssociationOverrides;
 use Doctrine\ORM\Mapping\Column;
 use Doctrine\ORM\Mapping\Entity;
 use Doctrine\ORM\Mapping\JoinColumn;
-use Doctrine\ORM\Mapping\ManyToOne;
 use Doctrine\ORM\Mapping\OneToMany;
 use Doctrine\ORM\Mapping\OneToOne;
 
@@ -19,6 +20,17 @@
  * Installation into organ.
  */
 #[Entity]
+#[AssociationOverrides([
+    new AssociationOverride(
+        name: 'member',
+        joinColumns: new JoinColumn(
+            name: 'lidnr',
+            referencedColumnName: 'lidnr',
+            nullable: false,
+        ),
+        inversedBy: 'installations',
+    ),
+])]
 class Installation extends FoundationReference
 {
     /**
@@ -27,19 +39,6 @@ class Installation extends FoundationReference
     #[Column(type: 'string')]
     protected string $function;
 
-    /**
-     * Member.
-     */
-    #[ManyToOne(
-        targetEntity: Member::class,
-        inversedBy: 'installations',
-    )]
-    #[JoinColumn(
-        name: 'lidnr',
-        referencedColumnName: 'lidnr',
-    )]
-    protected Member $member;
-
     /**
      * Reappointment subdecisions if this installation was prolonged (can be done multiple times).
      *
@@ -92,20 +91,14 @@ public function setFunction(string $function): void
 
     /**
      * Get the member.
+     *
+     * @psalm-suppress InvalidNullableReturnType
      */
     public function getMember(): Member
     {
         return $this->member;
     }
 
-    /**
-     * Set the member.
-     */
-    public function setMember(Member $member): void
-    {
-        $this->member = $member;
-    }
-
     /**
      * Get the reappointments, if they exist.
      *
diff --git a/module/Decision/src/Model/SubDecision/Key/Granting.php b/module/Decision/src/Model/SubDecision/Key/Granting.php
index 4dee5a44c9..7b5bba226a 100644
--- a/module/Decision/src/Model/SubDecision/Key/Granting.php
+++ b/module/Decision/src/Model/SubDecision/Key/Granting.php
@@ -10,24 +10,11 @@
 use Decision\Model\SubDecision;
 use Doctrine\ORM\Mapping\Column;
 use Doctrine\ORM\Mapping\Entity;
-use Doctrine\ORM\Mapping\JoinColumn;
-use Doctrine\ORM\Mapping\ManyToOne;
 use Doctrine\ORM\Mapping\OneToOne;
 
 #[Entity]
 class Granting extends SubDecision
 {
-    /**
-     * The member who is granted a keycode of GEWIS.
-     */
-    #[ManyToOne(targetEntity: Member::class)]
-    #[JoinColumn(
-        name: 'lidnr',
-        referencedColumnName: 'lidnr',
-        nullable: true,
-    )]
-    protected ?Member $grantee = null;
-
     /**
      * Till when the keycode is granted.
      */
@@ -52,22 +39,6 @@ class Granting extends SubDecision
     )]
     protected Keyholder $keyholder;
 
-    /**
-     * Get the grantee.
-     */
-    public function getGrantee(): ?Member
-    {
-        return $this->grantee;
-    }
-
-    /**
-     * Set the grantee.
-     */
-    public function setGrantee(Member $grantee): void
-    {
-        $this->grantee = $grantee;
-    }
-
     /**
      * Get the date.
      */