diff --git a/src/mutmut/mutation/mutators.py b/src/mutmut/mutation/mutators.py
index 40b074d9..d6fa5252 100644
--- a/src/mutmut/mutation/mutators.py
+++ b/src/mutmut/mutation/mutators.py
@@ -1,5 +1,7 @@
 """This module contains the mutations for indidvidual nodes, e.g. replacing a != b with a == b."""
 
+import cmath
+import math
 import re
 from collections.abc import Callable
 from collections.abc import Iterable
@@ -22,10 +24,19 @@
 
 
 def operator_number(node: cst.BaseNumber) -> Iterable[cst.BaseNumber]:
+    # A float literal too large for a float, like 1e999 (a common way to spell
+    # infinity), evaluates to inf. inf + 1 is still inf, which has no literal
+    # form, so there is no number mutant to make.
     if isinstance(node, cst.Integer | cst.Float):
-        yield node.with_changes(value=repr(node.evaluated_value + 1))
+        value = node.evaluated_value + 1
+        if isinstance(value, float) and math.isinf(value):
+            return
+        yield node.with_changes(value=repr(value))
     elif isinstance(node, cst.Imaginary):
-        yield node.with_changes(value=repr(node.evaluated_value + 1j))
+        complex_value = node.evaluated_value + 1j
+        if cmath.isinf(complex_value):
+            return
+        yield node.with_changes(value=repr(complex_value))
     else:
         print("Unexpected number type", node)
 
diff --git a/tests/mutation/test_mutation.py b/tests/mutation/test_mutation.py
index 0ff0d198..8ee2a644 100644
--- a/tests/mutation/test_mutation.py
+++ b/tests/mutation/test_mutation.py
@@ -299,6 +299,11 @@ def mutated_module(source: str) -> str:
         ("1.0j", "2j"),
         ("0o1", "2"),
         ("1.0e10", "10000000001.0"),
+        # too large for a float, so they evaluate to inf, which has no literal form
+        ("1e999", []),
+        ("1e999j", []),
+        ("a = 1e999", "a = None"),
+        ("1.5e400 + 2", ["1.5e400 - 2", "1.5e400 + 3"]),
         ("a = {x for x in y}", "a = None"),
         ("x+=1", ["x = 1", "x -= 1", "x+=2"]),
         ("x-=1", ["x = 1", "x += 1", "x-=2"]),