diff --git a/exercises/practice/flower-field/.meta/tests.toml b/exercises/practice/flower-field/.meta/tests.toml
index c2b24fda..965ba8fd 100644
--- a/exercises/practice/flower-field/.meta/tests.toml
+++ b/exercises/practice/flower-field/.meta/tests.toml
@@ -44,3 +44,6 @@ description = "cross"
 
 [dd9d4ca8-9e68-4f78-a677-a2a70fd7a7b8]
 description = "large garden"
+
+[6e4ac13a-3e43-4728-a2e3-3551d4b1a996]
+description = "multiple adjacent flowers"
diff --git a/exercises/practice/flower-field/source/flower_field.d b/exercises/practice/flower-field/source/flower_field.d
index 4c7d4f3f..d0f13cb0 100644
--- a/exercises/practice/flower-field/source/flower_field.d
+++ b/exercises/practice/flower-field/source/flower_field.d
@@ -46,7 +46,7 @@ unittest
             assert(annotate(garden) == expected);
         }
 
-        // garden with only flowers
+        // Garden full of flowers
         {
             immutable string[] garden = [
                 "***",
@@ -190,5 +190,16 @@ unittest
             ];
             assert(annotate(garden) == expected);
         }
+
+        // Multiple adjacent flowers
+        {
+            immutable string[] garden = [
+                " ** ",
+            ];
+            string[] expected = [
+                "1**1",
+            ];
+            assert(annotate(garden) == expected);
+        }
     }
 }
diff --git a/exercises/practice/isbn-verifier/.meta/tests.toml b/exercises/practice/isbn-verifier/.meta/tests.toml
index 6d5a8459..17e18d47 100644
--- a/exercises/practice/isbn-verifier/.meta/tests.toml
+++ b/exercises/practice/isbn-verifier/.meta/tests.toml
@@ -30,6 +30,12 @@ description = "invalid character in isbn is not treated as zero"
 [28025280-2c39-4092-9719-f3234b89c627]
 description = "X is only valid as a check digit"
 
+[8005b57f-f194-44ee-88d2-a77ac4142591]
+description = "only one check digit is allowed"
+
+[fdb14c99-4cf8-43c5-b06d-eb1638eff343]
+description = "X is not substituted by the value 10"
+
 [f6294e61-7e79-46b3-977b-f48789a4945b]
 description = "valid isbn without separating dashes"
 
diff --git a/exercises/practice/isbn-verifier/source/isbn_verifier.d b/exercises/practice/isbn-verifier/source/isbn_verifier.d
index daf0b3a7..facdc5b8 100644
--- a/exercises/practice/isbn-verifier/source/isbn_verifier.d
+++ b/exercises/practice/isbn-verifier/source/isbn_verifier.d
@@ -32,6 +32,12 @@ unittest
         // X is only valid as a check digit
         assert(!isValid("3-598-2X507-9"));
 
+        // Only one check digit is allowed
+        assert(!isValid("3-598-21508-96"));
+
+        // X is not substituted by the value 10
+        assert(!isValid("3-598-2X507-5"));
+
         // Valid isbn without separating dashes
         assert(isValid("3598215088"));
 
diff --git a/exercises/practice/line-up/.docs/instructions.md b/exercises/practice/line-up/.docs/instructions.md
index fb41d4cb..9e686ecb 100644
--- a/exercises/practice/line-up/.docs/instructions.md
+++ b/exercises/practice/line-up/.docs/instructions.md
@@ -5,9 +5,9 @@ Yaʻqūb expects to use numbers from 1 up to 999.
 
 Rules:
 
-- Numbers ending in 1 (except for 11) → `"st"`
-- Numbers ending in 2 (except for 12) → `"nd"`
-- Numbers ending in 3 (except for 13) → `"rd"`
+- Numbers ending in 1 (unless ending in 11) → `"st"`
+- Numbers ending in 2 (unless ending in 12) → `"nd"`
+- Numbers ending in 3 (unless ending in 13) → `"rd"`
 - All other numbers → `"th"`
 
 Examples:
diff --git a/exercises/practice/triangle/.docs/instructions.md b/exercises/practice/triangle/.docs/instructions.md
index ac390087..e9b053dc 100644
--- a/exercises/practice/triangle/.docs/instructions.md
+++ b/exercises/practice/triangle/.docs/instructions.md
@@ -13,6 +13,12 @@ A _scalene_ triangle has all sides of different lengths.
 
 For a shape to be a triangle at all, all sides have to be of length > 0, and the sum of the lengths of any two sides must be greater than or equal to the length of the third side.
 
+~~~~exercism/note
+_Degenerate triangles_ are triangles where the sum of the length of two sides is **equal** to the length of the third side, e.g. `1, 1, 2`.
+We opted to not include tests for degenerate triangles in this exercise.
+You may handle those situations if you wish to do so, or safely ignore them.
+~~~~
+
 In equations:
 
 Let `a`, `b`, and `c` be sides of the triangle.