diff --git a/prymer/offtarget/offtarget_detector.py b/prymer/offtarget/offtarget_detector.py
index 659cf27..34b5d9e 100644
--- a/prymer/offtarget/offtarget_detector.py
+++ b/prymer/offtarget/offtarget_detector.py
@@ -225,6 +225,8 @@ def __init__(
 
         Raises:
             ValueError: If `max_amplicon_size` is not greater than 0.
+            ValueError: If `min_amplicon_size` is outside the range 1 to `max_amplicon_size`,
+                inclusive.
             ValueError: If any of `max_primer_hits`, `max_primer_pair_hits`, or
                 `min_primer_pair_hits` are not greater than or equal to 0.
             ValueError: If `three_prime_region_length` is not greater than 0.
@@ -235,6 +237,11 @@ def __init__(
         errors: list[str] = []
         if max_amplicon_size < 1:
             errors.append(f"'max_amplicon_size' must be greater than 0. Saw {max_amplicon_size}")
+        if min_amplicon_size < 1 or min_amplicon_size > max_amplicon_size:
+            errors.append(
+                f"'min_amplicon_size' must be between 1 and 'max_amplicon_size'={max_amplicon_size}"
+                f" inclusive. Saw {min_amplicon_size}"
+            )
         if max_primer_hits < 0:
             errors.append(
                 f"'max_primer_hits' must be greater than or equal to 0. Saw {max_primer_hits}"
@@ -292,33 +299,6 @@ def __init__(
         self._keep_spans: bool = keep_spans
         self._keep_primer_spans: bool = keep_primer_spans
 
-    def __post_init__(self) -> None:
-        """
-        Validates parameters.
-
-        Raises:
-            ValueError: If `min_amplicon_size` is greater than `max_amplicon_size`, or if either
-                value is less than 1.
-            ValueError: If `max_primer_hits`, `max_primer_pair_hits`, or `min_primer_pair_hits` are
-                less than 0.
-        """
-        errors: list[str] = []
-        if self._min_amplicon_size < 1:
-            errors.append("'min_amplicon_size' must be greater than or equal to 1.")
-        if self._max_amplicon_size < 1:
-            errors.append("'max_amplicon_size' must be greater than or equal to 1.")
-        if self._min_amplicon_size > self._max_amplicon_size:
-            errors.append("'min_amplicon_size' must be less than or equal to 'max_amplicon_size'.")
-        if self._max_primer_hits < 0:
-            errors.append("'max_primer_hits' must be greater than or equal to 0.")
-        if self._max_primer_pair_hits < 0:
-            errors.append("'max_primer_pair_hits' must be greater than or equal to 0.")
-        if self._min_primer_pair_hits < 0:
-            errors.append("'min_primer_pair_hits' must be greater than or equal to 0.")
-
-        if len(errors) > 0:
-            raise ValueError("\n".join(errors))
-
     def filter(self, primers: list[PrimerType]) -> list[PrimerType]:
         """
         Remove primers that have more than `max_primer_hits` mappings to the genome.
diff --git a/tests/offtarget/test_offtarget.py b/tests/offtarget/test_offtarget.py
index 8924e41..8aa7692 100644
--- a/tests/offtarget/test_offtarget.py
+++ b/tests/offtarget/test_offtarget.py
@@ -428,17 +428,20 @@ class CustomPrimer(Oligo):
 @pytest.mark.parametrize(
     (
         "max_primer_hits,max_primer_pair_hits,min_primer_pair_hits,three_prime_region_length,"
-        "max_mismatches_in_three_prime_region,max_mismatches,max_amplicon_size,expected_error"
+        "max_mismatches_in_three_prime_region,max_mismatches,max_amplicon_size,min_amplicon_size,"
+        "expected_error"
     ),
     [
-        (-1, 1, 1, 20, 0, 0, 1, "'max_primer_hits' must be greater than or equal to 0. Saw -1"),
-        (1, -1, 1, 20, 0, 0, 1, "'max_primer_pair_hits' must be greater than or equal to 0. Saw -1"),  # noqa: E501
-        (1, 1, -1, 20, 0, 0, 1, "'min_primer_pair_hits' must be greater than or equal to 0. Saw -1"),  # noqa: E501
-        (1, 1, 1, 0, 0, 0, 1, "'three_prime_region_length' must be greater than 0. Saw 0"),
-        (1, 1, 1, 20, -1, 0, 1, "'max_mismatches_in_three_prime_region' must be between 0 and 20 inclusive. Saw -1"),  # noqa: E501
-        (1, 1, 1, 20, 21, 0, 1, "'max_mismatches_in_three_prime_region' must be between 0 and 20 inclusive. Saw 21"),  # noqa: E501
-        (1, 1, 1, 20, 0, -1, 1, "'max_mismatches' must be greater than or equal to 0. Saw -1"),
-        (1, 1, 1, 20, 0, 0, 0, "'max_amplicon_size' must be greater than 0. Saw 0"),
+        (-1, 1, 1, 20, 0, 0, 1, 1, "'max_primer_hits' must be greater than or equal to 0. Saw -1"),
+        (1, -1, 1, 20, 0, 0, 1, 1, "'max_primer_pair_hits' must be greater than or equal to 0. Saw -1"),  # noqa: E501
+        (1, 1, -1, 20, 0, 0, 1, 1, "'min_primer_pair_hits' must be greater than or equal to 0. Saw -1"),  # noqa: E501
+        (1, 1, 1, 0, 0, 0, 1, 1, "'three_prime_region_length' must be greater than 0. Saw 0"),
+        (1, 1, 1, 20, -1, 0, 1, 1, "'max_mismatches_in_three_prime_region' must be between 0 and 20 inclusive. Saw -1"),  # noqa: E501
+        (1, 1, 1, 20, 21, 0, 1, 1, "'max_mismatches_in_three_prime_region' must be between 0 and 20 inclusive. Saw 21"),  # noqa: E501
+        (1, 1, 1, 20, 0, -1, 1, 1, "'max_mismatches' must be greater than or equal to 0. Saw -1"),
+        (1, 1, 1, 20, 0, 0, 0, 1, "'max_amplicon_size' must be greater than 0. Saw 0"),
+        (1, 1, 1, 20, 0, 0, 10, 0, "'min_amplicon_size' must be between 1 and 'max_amplicon_size'=10 inclusive. Saw 0"),  # noqa: E501
+        (1, 1, 1, 20, 0, 0, 10, 11, "'min_amplicon_size' must be between 1 and 'max_amplicon_size'=10 inclusive. Saw 11"),  # noqa: E501
     ],
 )
 # fmt: on
@@ -451,6 +454,7 @@ def test_init(
     max_mismatches_in_three_prime_region: int,
     max_mismatches: int,
     max_amplicon_size: int,
+    min_amplicon_size: int,
     expected_error: str,
 ) -> None:
     with pytest.raises(ValueError, match=expected_error):
@@ -463,4 +467,5 @@ def test_init(
             max_mismatches_in_three_prime_region=max_mismatches_in_three_prime_region,
             max_mismatches=max_mismatches,
             max_amplicon_size=max_amplicon_size,
+            min_amplicon_size=min_amplicon_size,
         )