diff --git a/doc/sinter_api.md b/doc/sinter_api.md
index a29c5b19..f91a8176 100644
--- a/doc/sinter_api.md
+++ b/doc/sinter_api.md
@@ -852,7 +852,7 @@ def to_csv_line(
         >>> print(sinter.CSV_HEADER)
              shots,    errors,  discards, seconds,decoder,strong_id,json_metadata,custom_counts
         >>> print(stat.to_csv_line())
-                22,         3,         0,       5,pymatching,test,"{""a"":[1,2,3]}",
+                22,         3,         0,       5.00,pymatching,test,"{""a"":[1,2,3]}",
     """
 ```
 
diff --git a/glue/sample/src/sinter/_data/_anon_task_stats.py b/glue/sample/src/sinter/_data/_anon_task_stats.py
index 60fee918..42281c07 100644
--- a/glue/sample/src/sinter/_data/_anon_task_stats.py
+++ b/glue/sample/src/sinter/_data/_anon_task_stats.py
@@ -1,6 +1,7 @@
 import collections
 import dataclasses
 from typing import Counter, Union, TYPE_CHECKING
+import numpy as np
 
 if TYPE_CHECKING:
     from sinter._data._task_stats import TaskStats
@@ -34,16 +35,16 @@ class AnonTaskStats:
     custom_counts: Counter[str] = dataclasses.field(default_factory=collections.Counter)
 
     def __post_init__(self):
-        assert isinstance(self.errors, int)
-        assert isinstance(self.shots, int)
-        assert isinstance(self.discards, int)
-        assert isinstance(self.seconds, (int, float))
+        assert isinstance(self.errors, (int, np.integer))
+        assert isinstance(self.shots, (int, np.integer))
+        assert isinstance(self.discards, (int, np.integer))
+        assert isinstance(self.seconds, (int, float, np.integer, np.floating))
         assert isinstance(self.custom_counts, collections.Counter)
         assert self.errors >= 0
         assert self.discards >= 0
         assert self.seconds >= 0
         assert self.shots >= self.errors + self.discards
-        assert all(isinstance(k, str) and isinstance(v, int) for k, v in self.custom_counts.items())
+        assert all(isinstance(k, str) and isinstance(v, (int, np.integer)) for k, v in self.custom_counts.items())
 
     def __repr__(self) -> str:
         terms = []
diff --git a/glue/sample/src/sinter/_data/_csv_out.py b/glue/sample/src/sinter/_data/_csv_out.py
index 2feb0fa2..535b9abe 100644
--- a/glue/sample/src/sinter/_data/_csv_out.py
+++ b/glue/sample/src/sinter/_data/_csv_out.py
@@ -36,6 +36,9 @@ def csv_line(*,
                                    separators=(',', ':'),
                                    sort_keys=True)
         if custom_counts:
+            # Ensure all custom_counts values are integers before dumping to JSON
+            for k in custom_counts:
+                custom_counts[k] = int(custom_counts[k])
             custom_counts = escape_csv(
                 json.dumps(custom_counts,
                            separators=(',', ':'),
diff --git a/glue/sample/src/sinter/_data/_task_stats.py b/glue/sample/src/sinter/_data/_task_stats.py
index 4d846e89..f184e94d 100644
--- a/glue/sample/src/sinter/_data/_task_stats.py
+++ b/glue/sample/src/sinter/_data/_task_stats.py
@@ -4,7 +4,7 @@
 from typing import Optional
 from typing import Union
 from typing import overload
-
+import numpy as np
 from sinter._data._anon_task_stats import AnonTaskStats
 from sinter._data._csv_out import csv_line
 
@@ -71,10 +71,10 @@ class TaskStats:
     custom_counts: Counter[str] = dataclasses.field(default_factory=collections.Counter)
 
     def __post_init__(self):
-        assert isinstance(self.errors, int)
-        assert isinstance(self.shots, int)
-        assert isinstance(self.discards, int)
-        assert isinstance(self.seconds, (int, float))
+        assert isinstance(self.errors, (int, np.integer))
+        assert isinstance(self.shots, (int, np.integer))
+        assert isinstance(self.discards, (int, np.integer))
+        assert isinstance(self.seconds, (int, float, np.integer, np.floating))
         assert isinstance(self.custom_counts, collections.Counter)
         assert isinstance(self.decoder, str)
         assert isinstance(self.strong_id, str)
@@ -83,7 +83,7 @@ def __post_init__(self):
         assert self.discards >= 0
         assert self.seconds >= 0
         assert self.shots >= self.errors + self.discards
-        assert all(isinstance(k, str) and isinstance(v, int) for k, v in self.custom_counts.items())
+        assert all(isinstance(k, str) and isinstance(v, (int, np.integer)) for k, v in self.custom_counts.items())
 
     def with_edits(
         self,
@@ -190,13 +190,13 @@ def to_csv_line(self) -> str:
             >>> print(sinter.CSV_HEADER)
                  shots,    errors,  discards, seconds,decoder,strong_id,json_metadata,custom_counts
             >>> print(stat.to_csv_line())
-                    22,         3,         0,       5,pymatching,test,"{""a"":[1,2,3]}",
+                    22,         3,         0,    5.00,pymatching,test,"{""a"":[1,2,3]}",
         """
         return csv_line(
-            shots=self.shots,
-            errors=self.errors,
-            seconds=self.seconds,
-            discards=self.discards,
+            shots=int(self.shots),
+            errors=int(self.errors),
+            seconds=float(self.seconds),
+            discards=int(self.discards),
             strong_id=self.strong_id,
             decoder=self.decoder,
             json_metadata=self.json_metadata,
diff --git a/glue/sample/src/sinter/_data/_task_stats_test.py b/glue/sample/src/sinter/_data/_task_stats_test.py
index 4060c2f1..79f456f2 100644
--- a/glue/sample/src/sinter/_data/_task_stats_test.py
+++ b/glue/sample/src/sinter/_data/_task_stats_test.py
@@ -29,7 +29,7 @@ def test_to_csv_line():
         discards=4,
         seconds=5,
     )
-    assert v.to_csv_line() == str(v) == '        22,         3,         4,       5,pymatching,test,"{""a"":[1,2,3]}",'
+    assert v.to_csv_line() == str(v) == '        22,         3,         4,    5.00,pymatching,test,"{""a"":[1,2,3]}",'
 
 
 def test_to_anon_stats():