diff --git a/prymer/api/picking.py b/prymer/api/picking.py
index 796628e..fa00ae2 100644
--- a/prymer/api/picking.py
+++ b/prymer/api/picking.py
@@ -143,7 +143,8 @@ def build_primer_pairs(
             for rp in right_primers:
                 amp_span = PrimerPair.calculate_amplicon_span(lp, rp)
 
-                if amp_span.length > amplicon_sizes.max:
+                # Ignore pairings with amplicon sizes out of the range specified
+                if not amplicon_sizes.min <= amp_span.length <= amplicon_sizes.max:
                     continue
 
                 # Since the amplicon span and the region_start are both 1-based, the minuend
diff --git a/tests/api/test_picking.py b/tests/api/test_picking.py
index cdb5da0..e69e5d0 100644
--- a/tests/api/test_picking.py
+++ b/tests/api/test_picking.py
@@ -292,6 +292,7 @@ def test_build_primers_amplicon_size_filtering(
         assert pair.amplicon.end == pair.right_primer.span.end
         assert pair.bases == REF_BASES[pair.amplicon.start - 1 : pair.amplicon.end]
         assert pair.span.length <= 200
+        assert pair.span.length >= 100
 
 
 def test_build_primers_heterodimer_filtering(