diff --git a/rts/FileLock.c b/rts/FileLock.c
index cd2dc1d1dc627ed78b039e61a9792d564ee59dee..f8e11ee1bf33db44ea8796f55fdeff95d00f1d57 100644
--- a/rts/FileLock.c
+++ b/rts/FileLock.c
@@ -41,7 +41,7 @@ static int cmpLocks(StgWord w1, StgWord w2)
     return (l1->device == l2->device && l1->inode == l2->inode);
 }
 
-static int hashLock(HashTable *table, StgWord w)
+static int hashLock(const HashTable *table, StgWord w)
 {
     Lock *l = (Lock *)w;
     StgWord key = l->inode ^ (l->inode >> 32) ^ l->device ^ (l->device >> 32);
diff --git a/rts/Hash.c b/rts/Hash.c
index aab3b2361bf1899a1bb293006543509e5d13e79d..b0939c49bcd456bb3446ee9306091e61bc5c53df 100644
--- a/rts/Hash.c
+++ b/rts/Hash.c
@@ -58,7 +58,7 @@ struct hashtable {
  * -------------------------------------------------------------------------- */
 
 int
-hashWord(HashTable *table, StgWord key)
+hashWord(const HashTable *table, StgWord key)
 {
     int bucket;
 
@@ -76,7 +76,7 @@ hashWord(HashTable *table, StgWord key)
 }
 
 int
-hashStr(HashTable *table, char *key)
+hashStr(const HashTable *table, char *key)
 {
     int h, bucket;
     char *s;
@@ -187,7 +187,7 @@ expand(HashTable *table)
 }
 
 void *
-lookupHashTable(HashTable *table, StgWord key)
+lookupHashTable(const HashTable *table, StgWord key)
 {
     int bucket;
     int segment;
diff --git a/rts/Hash.h b/rts/Hash.h
index 136f94a18cf0dab06a6ed9e592e6ac87d5cb716a..c2dfc26d6da7574d790818c9a239daa5f8757d07 100644
--- a/rts/Hash.h
+++ b/rts/Hash.h
@@ -15,7 +15,7 @@ typedef struct hashtable HashTable; /* abstract */
 
 /* Hash table access where the keys are StgWords */
 HashTable * allocHashTable    ( void );
-void *      lookupHashTable ( HashTable *table, StgWord key );
+void *      lookupHashTable ( const HashTable *table, StgWord key );
 void        insertHashTable ( HashTable *table, StgWord key, void *data );
 void *      removeHashTable ( HashTable *table, StgWord key, void *data );
 
@@ -44,11 +44,11 @@ HashTable * allocStrHashTable ( void );
    (removeHashTable(table, (StgWord)key, data))
 
 /* Hash tables for arbitrary keys */
-typedef int HashFunction(HashTable *table, StgWord key);
+typedef int HashFunction(const HashTable *table, StgWord key);
 typedef int CompareFunction(StgWord key1, StgWord key2);
 HashTable * allocHashTable_(HashFunction *hash, CompareFunction *compare);
-int hashWord(HashTable *table, StgWord key);
-int hashStr(HashTable *table, char *key);
+int hashWord(const HashTable *table, StgWord key);
+int hashStr(const HashTable *table, char *key);
 
 /* Freeing hash tables
  */