diff --git a/Action.c b/Action.c
index 11e87009..822c9174 100644
--- a/Action.c
+++ b/Action.c
@@ -100,7 +100,7 @@ static bool changePriority(MainPanel* panel, int delta) {
    return anyTagged;
 }
 
-static void addUserToVector(int key, void* userCast, void* panelCast) {
+static void addUserToVector(hkey_t key, void* userCast, void* panelCast) {
    const char* user = userCast;
    Panel* panel = panelCast;
    Panel_add(panel, (Object*) ListItem_new(user, key));
diff --git a/Hashtable.c b/Hashtable.c
index 92337822..606dfd60 100644
--- a/Hashtable.c
+++ b/Hashtable.c
@@ -14,9 +14,9 @@ in the source distribution for its full text.
 
 #ifndef NDEBUG
 
-static bool Hashtable_isConsistent(Hashtable* this) {
-   int items = 0;
-   for (int i = 0; i < this->size; i++) {
+static bool Hashtable_isConsistent(const Hashtable* this) {
+   unsigned int items = 0;
+   for (unsigned int i = 0; i < this->size; i++) {
       HashtableItem* bucket = this->buckets[i];
       while (bucket) {
          items++;
@@ -26,9 +26,9 @@ static bool Hashtable_isConsistent(Hashtable* this) {
    return items == this->items;
 }
 
-int Hashtable_count(Hashtable* this) {
-   int items = 0;
-   for (int i = 0; i < this->size; i++) {
+unsigned int Hashtable_count(const Hashtable* this) {
+   unsigned int items = 0;
+   for (unsigned int i = 0; i < this->size; i++) {
       HashtableItem* bucket = this->buckets[i];
       while (bucket) {
          items++;
@@ -41,7 +41,7 @@ int Hashtable_count(Hashtable* this) {
 
 #endif /* NDEBUG */
 
-static HashtableItem* HashtableItem_new(unsigned int key, void* value) {
+static HashtableItem* HashtableItem_new(hkey_t key, void* value) {
    HashtableItem* this;
 
    this = xMalloc(sizeof(HashtableItem));
@@ -51,7 +51,7 @@ static HashtableItem* HashtableItem_new(unsigned int key, void* value) {
    return this;
 }
 
-Hashtable* Hashtable_new(int size, bool owner) {
+Hashtable* Hashtable_new(unsigned int size, bool owner) {
    Hashtable* this;
 
    this = xMalloc(sizeof(Hashtable));
@@ -65,7 +65,7 @@ Hashtable* Hashtable_new(int size, bool owner) {
 
 void Hashtable_delete(Hashtable* this) {
    assert(Hashtable_isConsistent(this));
-   for (int i = 0; i < this->size; i++) {
+   for (unsigned int i = 0; i < this->size; i++) {
       HashtableItem* walk = this->buckets[i];
       while (walk != NULL) {
          if (this->owner)
@@ -80,7 +80,7 @@ void Hashtable_delete(Hashtable* this) {
    free(this);
 }
 
-void Hashtable_put(Hashtable* this, unsigned int key, void* value) {
+void Hashtable_put(Hashtable* this, hkey_t key, void* value) {
    unsigned int index = key % this->size;
    HashtableItem** bucketPtr = &(this->buckets[index]);
    while (true)
@@ -101,7 +101,7 @@ void Hashtable_put(Hashtable* this, unsigned int key, void* value) {
    assert(Hashtable_isConsistent(this));
 }
 
-void* Hashtable_remove(Hashtable* this, unsigned int key) {
+void* Hashtable_remove(Hashtable* this, hkey_t key) {
    unsigned int index = key % this->size;
 
    assert(Hashtable_isConsistent(this));
@@ -128,7 +128,7 @@ void* Hashtable_remove(Hashtable* this, unsigned int key) {
    return NULL;
 }
 
-void* Hashtable_get(Hashtable* this, unsigned int key) {
+void* Hashtable_get(Hashtable* this, hkey_t key) {
    unsigned int index = key % this->size;
    HashtableItem* bucketPtr = this->buckets[index];
    while (true) {
@@ -146,7 +146,7 @@ void* Hashtable_get(Hashtable* this, unsigned int key) {
 
 void Hashtable_foreach(Hashtable* this, Hashtable_PairFunction f, void* userData) {
    assert(Hashtable_isConsistent(this));
-   for (int i = 0; i < this->size; i++) {
+   for (unsigned int i = 0; i < this->size; i++) {
       HashtableItem* walk = this->buckets[i];
       while (walk != NULL) {
          f(walk->key, walk->value, userData);
diff --git a/Hashtable.h b/Hashtable.h
index dcdc89fe..15af9e0d 100644
--- a/Hashtable.h
+++ b/Hashtable.h
@@ -10,36 +10,38 @@ in the source distribution for its full text.
 #include <stdbool.h>
 
 
-typedef void(*Hashtable_PairFunction)(int, void*, void*);
+typedef unsigned int hkey_t;
 
-typedef struct HashtableItem {
-   unsigned int key;
+typedef void(*Hashtable_PairFunction)(hkey_t key, void* value, void* userdata);
+
+typedef struct HashtableItem_ {
+   hkey_t key;
    void* value;
-   struct HashtableItem* next;
+   struct HashtableItem_* next;
 } HashtableItem;
 
 typedef struct Hashtable_ {
-   int size;
+   unsigned int size;
    HashtableItem** buckets;
-   int items;
+   unsigned int items;
    bool owner;
 } Hashtable;
 
 #ifndef NDEBUG
 
-int Hashtable_count(Hashtable* this);
+unsigned int Hashtable_count(const Hashtable* this);
 
 #endif /* NDEBUG */
 
-Hashtable* Hashtable_new(int size, bool owner);
+Hashtable* Hashtable_new(unsigned int size, bool owner);
 
 void Hashtable_delete(Hashtable* this);
 
-void Hashtable_put(Hashtable* this, unsigned int key, void* value);
+void Hashtable_put(Hashtable* this, hkey_t key, void* value);
 
-void* Hashtable_remove(Hashtable* this, unsigned int key);
+void* Hashtable_remove(Hashtable* this, hkey_t key);
 
-void* Hashtable_get(Hashtable* this, unsigned int key);
+void* Hashtable_get(Hashtable* this, hkey_t key);
 
 void Hashtable_foreach(Hashtable* this, Hashtable_PairFunction f, void* userData);
 
diff --git a/Vector.c b/Vector.c
index 09d1612e..721ebdd3 100644
--- a/Vector.c
+++ b/Vector.c
@@ -60,14 +60,14 @@ static bool Vector_isConsistent(const Vector* this) {
    }
 }
 
-int Vector_count(const Vector* this) {
-   int items = 0;
+unsigned int Vector_count(const Vector* this) {
+   unsigned int items = 0;
    for (int i = 0; i < this->items; i++) {
       if (this->array[i]) {
          items++;
       }
    }
-   assert(items == this->items);
+   assert(items == (unsigned int)this->items);
    return items;
 }
 
diff --git a/Vector.h b/Vector.h
index 70688152..ec354b16 100644
--- a/Vector.h
+++ b/Vector.h
@@ -54,7 +54,7 @@ void Vector_set(Vector* this, int idx, void* data_);
 
 Object* Vector_get(Vector* this, int idx);
 int Vector_size(const Vector* this);
-int Vector_count(const Vector* this);
+unsigned int Vector_count(const Vector* this);
 
 #else /* NDEBUG */