diff --git a/src/vm/wren_core.wren b/src/vm/wren_core.wren
index 03a000b8..2788308c 100644
--- a/src/vm/wren_core.wren
+++ b/src/vm/wren_core.wren
@@ -56,9 +56,21 @@ class Sequence {
 
   map(transformation) { MapSequence.new(this, transformation) }
 
-  skip(count) { SkipSequence.new(this, count) }
+  skip(count) {
+    if (!(count is Num) || !count.isInteger || count < 0) {
+      Fiber.abort("Count must be a non-negative integer.")
+    }
 
-  take(count) { TakeSequence.new(this, count) }
+    return SkipSequence.new(this, count)
+  }
+
+  take(count) {
+    if (!(count is Num) || !count.isInteger || count < 0) {
+      Fiber.abort("Count must be a non-negative integer.")
+    }
+
+    return TakeSequence.new(this, count)
+  }
 
   where(predicate) { WhereSequence.new(this, predicate) }
 
@@ -173,9 +185,9 @@ class String is Sequence {
   bytes { StringByteSequence.new(this) }
   codePoints { StringCodePointSequence.new(this) }
 
-  split(delim) {
-    if (!(delim is String) || delim.isEmpty) {
-      Fiber.abort("Argument must be a non-empty string.")
+  split(delimiter) {
+    if (!(delimiter is String) || delimiter.isEmpty) {
+      Fiber.abort("Delimiter must be a non-empty string.")
     }
 
     var result = []
@@ -183,10 +195,10 @@ class String is Sequence {
     var last = 0
     var index = 0
 
-    var delimSize = delim.byteCount_
+    var delimSize = delimiter.byteCount_
     var size = byteCount_
 
-    while (last < size && (index = indexOf(delim, last)) != -1) {
+    while (last < size && (index = indexOf(delimiter, last)) != -1) {
       result.add(this[last...index])
       last = index + delimSize
     }
diff --git a/src/vm/wren_core.wren.inc b/src/vm/wren_core.wren.inc
index 079fed2f..8251f9f3 100644
--- a/src/vm/wren_core.wren.inc
+++ b/src/vm/wren_core.wren.inc
@@ -58,9 +58,21 @@ static const char* coreModuleSource =
 "\n"
 "  map(transformation) { MapSequence.new(this, transformation) }\n"
 "\n"
-"  skip(count) { SkipSequence.new(this, count) }\n"
+"  skip(count) {\n"
+"    if (!(count is Num) || !count.isInteger || count < 0) {\n"
+"      Fiber.abort(\"Count must be a non-negative integer.\")\n"
+"    }\n"
 "\n"
-"  take(count) { TakeSequence.new(this, count) }\n"
+"    return SkipSequence.new(this, count)\n"
+"  }\n"
+"\n"
+"  take(count) {\n"
+"    if (!(count is Num) || !count.isInteger || count < 0) {\n"
+"      Fiber.abort(\"Count must be a non-negative integer.\")\n"
+"    }\n"
+"\n"
+"    return TakeSequence.new(this, count)\n"
+"  }\n"
 "\n"
 "  where(predicate) { WhereSequence.new(this, predicate) }\n"
 "\n"
@@ -175,9 +187,9 @@ static const char* coreModuleSource =
 "  bytes { StringByteSequence.new(this) }\n"
 "  codePoints { StringCodePointSequence.new(this) }\n"
 "\n"
-"  split(delim) {\n"
-"    if (!(delim is String) || delim.isEmpty) {\n"
-"      Fiber.abort(\"Argument must be a non-empty string.\")\n"
+"  split(delimiter) {\n"
+"    if (!(delimiter is String) || delimiter.isEmpty) {\n"
+"      Fiber.abort(\"Delimiter must be a non-empty string.\")\n"
 "    }\n"
 "\n"
 "    var result = []\n"
@@ -185,10 +197,10 @@ static const char* coreModuleSource =
 "    var last = 0\n"
 "    var index = 0\n"
 "\n"
-"    var delimSize = delim.byteCount_\n"
+"    var delimSize = delimiter.byteCount_\n"
 "    var size = byteCount_\n"
 "\n"
-"    while (last < size && (index = indexOf(delim, last)) != -1) {\n"
+"    while (last < size && (index = indexOf(delimiter, last)) != -1) {\n"
 "      result.add(this[last...index])\n"
 "      last = index + delimSize\n"
 "    }\n"
diff --git a/test/core/sequence/skip.wren b/test/core/sequence/skip.wren
index b54a51fc..fabfca1e 100644
--- a/test/core/sequence/skip.wren
+++ b/test/core/sequence/skip.wren
@@ -15,14 +15,11 @@ var test = TestSequence.new().skip(0)
 System.print(test is Sequence) // expect: true
 System.print(test) // expect: instance of SkipSequence
 
-// Skipping 0 changes nothing
+// Skipping 0 changes nothing.
 System.print(test.toList) // expect: [1, 2, 3]
 
-// Skipping 1 works
+// Skipping 1 works.
 System.print(test.skip(1).toList) // expect: [2, 3]
 
-// Skipping more than length of sequence produces empty list
+// Skipping more than length of sequence produces empty list.
 System.print(test.skip(4).isEmpty) // expect: true
-
-// Skipping less than 0 changes nothing
-System.print(test.skip(-10).toList) // expect: [1, 2, 3]
diff --git a/test/core/sequence/skip_negative.wren b/test/core/sequence/skip_negative.wren
new file mode 100644
index 00000000..957a9504
--- /dev/null
+++ b/test/core/sequence/skip_negative.wren
@@ -0,0 +1 @@
+[1, 2, 3].skip(-1) // expect runtime error: Count must be a non-negative integer.
diff --git a/test/core/sequence/skip_not_int.wren b/test/core/sequence/skip_not_int.wren
new file mode 100644
index 00000000..de171f58
--- /dev/null
+++ b/test/core/sequence/skip_not_int.wren
@@ -0,0 +1 @@
+[1, 2, 3].skip(1.2) // expect runtime error: Count must be a non-negative integer.
diff --git a/test/core/sequence/skip_not_num.wren b/test/core/sequence/skip_not_num.wren
new file mode 100644
index 00000000..63dfe9b2
--- /dev/null
+++ b/test/core/sequence/skip_not_num.wren
@@ -0,0 +1 @@
+[1, 2, 3].skip("s") // expect runtime error: Count must be a non-negative integer.
diff --git a/test/core/sequence/take.wren b/test/core/sequence/take.wren
index 81c188e8..a8767845 100644
--- a/test/core/sequence/take.wren
+++ b/test/core/sequence/take.wren
@@ -15,14 +15,11 @@ var test = TestSequence.new().take(3)
 System.print(test is Sequence) // expect: true
 System.print(test) // expect: instance of TakeSequence
 
-// Taking 0 produces empty list
+// Taking 0 produces empty list.
 System.print(test.take(0).isEmpty) // expect: true
 
-// Taking 1 works
+// Taking 1 works.
 System.print(test.take(1).toList) // expect: [1]
 
-// Taking more than length of sequence produces whole sequence
+// Taking more than length of sequence produces whole sequence.
 System.print(test.take(4).toList) // expect: [1, 2, 3]
-
-// Taking less than 0 produces empty list
-System.print(test.take(-10).isEmpty) // expect: true
diff --git a/test/core/sequence/take_negative.wren b/test/core/sequence/take_negative.wren
new file mode 100644
index 00000000..5b98f021
--- /dev/null
+++ b/test/core/sequence/take_negative.wren
@@ -0,0 +1 @@
+[1, 2, 3].take(-1) // expect runtime error: Count must be a non-negative integer.
diff --git a/test/core/sequence/take_not_int.wren b/test/core/sequence/take_not_int.wren
new file mode 100644
index 00000000..d3e2452b
--- /dev/null
+++ b/test/core/sequence/take_not_int.wren
@@ -0,0 +1 @@
+[1, 2, 3].take(1.2) // expect runtime error: Count must be a non-negative integer.
diff --git a/test/core/sequence/take_not_num.wren b/test/core/sequence/take_not_num.wren
new file mode 100644
index 00000000..0a818a27
--- /dev/null
+++ b/test/core/sequence/take_not_num.wren
@@ -0,0 +1 @@
+[1, 2, 3].take("s") // expect runtime error: Count must be a non-negative integer.
diff --git a/test/core/string/split_argument_not_string.wren b/test/core/string/split_argument_not_string.wren
index c4fdd1af..424270db 100644
--- a/test/core/string/split_argument_not_string.wren
+++ b/test/core/string/split_argument_not_string.wren
@@ -1 +1 @@
-"foo".split(1) // expect runtime error: Argument must be a non-empty string.
+"foo".split(1) // expect runtime error: Delimiter must be a non-empty string.
diff --git a/test/core/string/split_empty_seperator.wren b/test/core/string/split_empty_seperator.wren
index ea211aaf..f6ff63fe 100644
--- a/test/core/string/split_empty_seperator.wren
+++ b/test/core/string/split_empty_seperator.wren
@@ -1 +1 @@
-"foo".split("") // expect runtime error: Argument must be a non-empty string.
+"foo".split("") // expect runtime error: Delimiter must be a non-empty string.