diff --git a/gallery_dl/text.py b/gallery_dl/text.py
index 2f18a616..7725ea09 100644
--- a/gallery_dl/text.py
+++ b/gallery_dl/text.py
@@ -209,11 +209,12 @@ def _hex_to_char(match):
 
 def parse_bytes(value, default=0, suffixes="bkmgtp"):
     """Convert a bytes-amount ("500k", "2.5M", ...) to int"""
-    try:
-        last = value[-1].lower()
-    except Exception:
+    if not value:
         return default
 
+    value = str(value).strip()
+    last = value[-1].lower()
+
     if last in suffixes:
         mul = 1024 ** suffixes.index(last)
         value = value[:-1]
diff --git a/gallery_dl/util.py b/gallery_dl/util.py
index 1f006a85..9fff88cb 100644
--- a/gallery_dl/util.py
+++ b/gallery_dl/util.py
@@ -898,25 +898,26 @@ def import_file(path):
         return __import__(name.replace("-", "_"))
 
 
-def build_duration_func(duration, min=0.0):
-    if not duration:
+def build_selection_func(value, min=0.0, conv=float):
+    if not value:
         if min:
             return lambda: min
         return None
 
-    if isinstance(duration, str):
-        lower, _, upper = duration.partition("-")
-        lower = float(lower)
+    if isinstance(value, str):
+        lower, _, upper = value.partition("-")
+        lower = conv(lower)
     else:
         try:
-            lower, upper = duration
+            lower, upper = value
         except TypeError:
-            lower, upper = duration, None
+            lower, upper = value, None
+        lower = conv(lower)
 
     if upper:
-        upper = float(upper)
+        upper = conv(upper)
         return functools.partial(
-            random.uniform,
+            random.uniform if min.__class__ is float else random.randint,
             lower if lower > min else min,
             upper if upper > min else min,
         )
@@ -926,6 +927,9 @@ def build_duration_func(duration, min=0.0):
         return lambda: lower
 
 
+build_duration_func = build_selection_func
+
+
 def build_extractor_filter(categories, negate=True, special=None):
     """Build a function that takes an Extractor class as argument
     and returns True if that class is allowed by 'categories'
diff --git a/test/test_text.py b/test/test_text.py
index 96656c1e..f20e3d00 100644
--- a/test/test_text.py
+++ b/test/test_text.py
@@ -359,6 +359,8 @@ class TestText(unittest.TestCase):
         )
 
     def test_parse_bytes(self, f=text.parse_bytes):
+        self.assertEqual(f(0), 0)
+        self.assertEqual(f(50), 50)
         self.assertEqual(f("0"), 0)
         self.assertEqual(f("50"), 50)
         self.assertEqual(f("50k"), 50 * 1024**1)
@@ -366,10 +368,13 @@ class TestText(unittest.TestCase):
         self.assertEqual(f("50g"), 50 * 1024**3)
         self.assertEqual(f("50t"), 50 * 1024**4)
         self.assertEqual(f("50p"), 50 * 1024**5)
+        self.assertEqual(f(" 50p "), 50 * 1024**5)
 
         # fractions
+        self.assertEqual(f(123.456), 123)
         self.assertEqual(f("123.456"), 123)
         self.assertEqual(f("123.567"), 124)
+        self.assertEqual(f(" 123.89 "), 124)
         self.assertEqual(f("0.5M"), round(0.5 * 1024**2))
 
         # invalid arguments
diff --git a/test/test_util.py b/test/test_util.py
index 7764114c..4561ce73 100644
--- a/test/test_util.py
+++ b/test/test_util.py
@@ -554,17 +554,21 @@ value = 123
         self.assertEqual(module.value, 123)
         self.assertIs(module.datetime, datetime)
 
-    def test_build_duration_func(self, f=util.build_duration_func):
+    def test_build_selection_func(self, f=util.build_selection_func):
 
-        def test_single(df, v):
+        def test_single(df, v, type=None):
             for _ in range(10):
                 self.assertEqual(df(), v)
+                if type is not None:
+                    self.assertIsInstance(df(), type)
 
-        def test_range(df, lower, upper):
+        def test_range(df, lower, upper, type=None):
             for __ in range(10):
                 v = df()
                 self.assertGreaterEqual(v, lower)
                 self.assertLessEqual(v, upper)
+                if type is not None:
+                    self.assertIsInstance(v, type)
 
         for v in (0, 0.0, "", None, (), []):
             self.assertIsNone(f(v))
@@ -572,16 +576,24 @@ value = 123
         for v in (0, 0.0, "", None, (), []):
             test_single(f(v, 1.0), 1.0)
 
-        test_single(f(3), 3)
-        test_single(f(3.0), 3.0)
-        test_single(f("3"), 3)
-        test_single(f("3.0-"), 3)
-        test_single(f("  3  -"), 3)
+        test_single(f(3)       , 3  , float)
+        test_single(f(3.0)     , 3.0, float)
+        test_single(f("3")     , 3  , float)
+        test_single(f("3.0-")  , 3  , float)
+        test_single(f("  3  -"), 3  , float)
 
-        test_range(f((2, 4)), 2, 4)
-        test_range(f([2, 4]), 2, 4)
-        test_range(f("2-4"), 2, 4)
-        test_range(f("  2.0  - 4 "), 2, 4)
+        test_range(f((2, 4))       , 2, 4, float)
+        test_range(f([2.0, 4.0])   , 2, 4, float)
+        test_range(f("2-4")        , 2, 4, float)
+        test_range(f("  2.0  - 4 "), 2, 4, float)
+
+        pb = text.parse_bytes
+        test_single(f("3", 0, pb)     , 3, int)
+        test_single(f("3.0-", 0, pb)  , 3, int)
+        test_single(f("  3  -", 0, pb), 3, int)
+
+        test_range(f("2k-4k", 0, pb)        , 2048, 4096, int)
+        test_range(f("  2.0k  - 4k ", 0, pb), 2048, 4096, int)
 
     def test_extractor_filter(self):
         # empty