diff --git a/qulab/scan/optimize.py b/qulab/scan/optimize.py
index 6b061024..bce79b91 100644
--- a/qulab/scan/optimize.py
+++ b/qulab/scan/optimize.py
@@ -37,8 +37,11 @@ def __init__(self, variables, **kwds):
                            self.config['method'])(self.instrum,
                                                   budget=self.config['budget'])
 
-    def suggest(self, *args, **kwds):
-        self.opt.suggest(*args, **kwds)
+    def suggest(self, *suggested):
+        suggested = [
+            space.transform(x) for x, space in zip(suggested, self.dimensions)
+        ]
+        self.opt.suggest(*suggested)
 
     def ask(self):
         tmp = self.opt.ask()
@@ -50,9 +53,9 @@ def ask(self):
     def tell(self, suggested: Sequence, value: Any):
         self._all_x.append(suggested)
         self._all_y.append(value)
-        suggested = [
+        suggested = tuple([
             space.transform(x) for x, space in zip(suggested, self.dimensions)
-        ]
+        ])
         # self.opt.suggest(*suggested)
         # x = self.opt.ask()
         x = self.instrum.spawn_child(new_value=(suggested, {}))
diff --git a/qulab/scan/scan.py b/qulab/scan/scan.py
index e0e7394c..922032a6 100644
--- a/qulab/scan/scan.py
+++ b/qulab/scan/scan.py
@@ -481,7 +481,8 @@ def search(self,
         elif isinstance(space, OptimizeSpace):
             space.name = name
             space.optimizer.dimensions[name] = space.space
-            space.optimizer.suggestions[name] = space.suggestions
+            if space.suggestions:
+                space.optimizer.suggestions[name] = space.suggestions
             self._add_search_space(name, space.optimizer.level, space)
             self.add_depends(space.optimizer.name, [name])
         else:
diff --git a/qulab/scan/space.py b/qulab/scan/space.py
index 6da81560..d56d697c 100644
--- a/qulab/scan/space.py
+++ b/qulab/scan/space.py
@@ -1,3 +1,4 @@
+import itertools
 from typing import Type
 
 import numpy as np
@@ -107,6 +108,9 @@ def __init__(self, optimizer: 'Optimizer', space, suggestions=None):
         self.optimizer = optimizer
         self.space = space
         self.name = None
+        if suggestions is not None and not isinstance(
+                suggestions, (list, tuple, np.ndarray)):
+            suggestions = [suggestions]
         self.suggestions = suggestions
 
     def __len__(self):
@@ -135,8 +139,17 @@ def __init__(self,
 
     def create(self):
         opt = self.method(list(self.dimensions.values()), **self.kwds)
-        for suggestion in zip([self.suggestions[key] for key in self.dimensions]):
-            opt.suggest(*suggestion)
+
+        def rvs(space):
+            while True:
+                yield space.rvs()[0]
+
+        if self.suggestions:
+            for suggestion in zip(*[
+                    self.suggestions.get(key, rvs(space))
+                    for key, space in self.dimensions.items()
+            ]):
+                opt.suggest(*suggestion)
         return opt
 
     def Categorical(self,