diff --git a/PGConnection.h b/PGConnection.h
index a4b7f65..ef16f53 100644
--- a/PGConnection.h
+++ b/PGConnection.h
@@ -18,8 +18,8 @@
 - (OFDictionary*)parameters;
 - (void)connect;
 - (void)reset;
-- (PGResult*)executeCommand: (OFString*)command;
-- (PGResult*)executeCommand: (OFString*)command
+- (PGResult*)executeCommand: (OFConstantString*)command;
+- (PGResult*)executeCommand: (OFConstantString*)command
 		 parameters: (id)firstParameter, ...;
 - (PGconn*)PG_connection;
 - (void)insertRow: (OFDictionary*)row
diff --git a/PGConnection.m b/PGConnection.m
index d2cb292..a09aaea 100644
--- a/PGConnection.m
+++ b/PGConnection.m
@@ -58,7 +58,7 @@
 	PQreset(conn);
 }
 
-- (PGResult*)executeCommand: (OFString*)command
+- (PGResult*)executeCommand: (OFConstantString*)command
 {
 	PGresult *result = PQexec(conn, [command UTF8String]);
 
@@ -77,7 +77,7 @@
 	return nil;
 }
 
-- (PGResult*)executeCommand: (OFString*)command
+- (PGResult*)executeCommand: (OFConstantString*)command
 		 parameters: (id)parameter, ...
 {
 	OFAutoreleasePool *pool = [[OFAutoreleasePool alloc] init];