diff --git a/src/digest/io_digest.cr b/src/digest/io_digest.cr
index 6789513cc847..0efcb56b7715 100644
--- a/src/digest/io_digest.cr
+++ b/src/digest/io_digest.cr
@@ -31,7 +31,7 @@ class IO::Digest < IO
   end
 
   def read(slice : Bytes) : Int32
-    read_bytes = io.read(slice)
+    read_bytes = io.read(slice).to_i32
     if @mode.read?
       digest_algorithm.update(slice[0, read_bytes])
     end
diff --git a/src/enumerable.cr b/src/enumerable.cr
index 130f926a2829..b9c3f587cfea 100644
--- a/src/enumerable.cr
+++ b/src/enumerable.cr
@@ -238,7 +238,7 @@ module Enumerable(T)
   # ```
   # [1, 2, 3, 4].count { |i| i % 2 == 0 } # => 2
   # ```
-  def count
+  def count(& : T -> _) : Int32
     count = 0
     each { |e| count += 1 if yield e }
     count
@@ -624,7 +624,7 @@ module Enumerable(T)
   # ```
   #
   # Returns `nil` if the block didn't return `true` for any element.
-  def index
+  def index(& : T -> _) : Int32?
     each_with_index do |e, i|
       return i if yield e
     end
@@ -638,7 +638,7 @@ module Enumerable(T)
   # ```
   #
   # Returns `nil` if *obj* is not in the collection.
-  def index(obj)
+  def index(obj) : Int32?
     index { |e| e == obj }
   end
 
diff --git a/src/http/content.cr b/src/http/content.cr
index ec7fe2bb252c..9bec0e66abda 100644
--- a/src/http/content.cr
+++ b/src/http/content.cr
@@ -60,7 +60,7 @@ module HTTP
 
     def read(slice : Bytes) : Int32
       ensure_send_continue
-      @io.read(slice)
+      @io.read(slice).to_i32
     end
 
     def read_byte : UInt8?
@@ -73,7 +73,7 @@ module HTTP
       @io.peek
     end
 
-    def skip(bytes_count) : Int32?
+    def skip(bytes_count) : Nil
       ensure_send_continue
       @io.skip(bytes_count)
     end
@@ -123,7 +123,7 @@ module HTTP
 
       to_read = Math.min(count, @chunk_remaining)
 
-      bytes_read = @io.read slice[0, to_read]
+      bytes_read = @io.read(slice[0, to_read]).to_i32
 
       if bytes_read == 0
         raise IO::EOFError.new("Invalid HTTP chunked content")
@@ -164,7 +164,7 @@ module HTTP
       peek
     end
 
-    def skip(bytes_count) : Int32?
+    def skip(bytes_count) : Nil
       ensure_send_continue
       if bytes_count <= @chunk_remaining
         @io.skip(bytes_count)
diff --git a/src/humanize.cr b/src/humanize.cr
index 251d1f563eb8..b7326b5076fc 100644
--- a/src/humanize.cr
+++ b/src/humanize.cr
@@ -82,7 +82,7 @@ struct Number
   end
 
   # :nodoc:
-  def self.prefix_index(i, group = 3) : Int32
+  def self.prefix_index(i : Int32, group : Int32 = 3) : Int32
     ((i - (i > 0 ? 1 : 0)) // group) * group
   end
 
diff --git a/src/io/hexdump.cr b/src/io/hexdump.cr
index b48d36ac8bfa..1ead92779cc0 100644
--- a/src/io/hexdump.cr
+++ b/src/io/hexdump.cr
@@ -26,8 +26,8 @@ class IO::Hexdump < IO
   def initialize(@io : IO, @output : IO = STDERR, @read = false, @write = false)
   end
 
-  def read(buf : Bytes)
-    @io.read(buf).tap do |read_bytes|
+  def read(buf : Bytes) : Int32
+    @io.read(buf).to_i32.tap do |read_bytes|
       buf[0, read_bytes].hexdump(@output) if @read && read_bytes
     end
   end
diff --git a/src/io/memory.cr b/src/io/memory.cr
index 2d3dbb5256ac..20e4ec0865c9 100644
--- a/src/io/memory.cr
+++ b/src/io/memory.cr
@@ -192,7 +192,7 @@ class IO::Memory < IO
   end
 
   # :nodoc:
-  def skip(bytes_count)
+  def skip(bytes_count) : Nil
     check_open
 
     available = @bytesize - @pos
diff --git a/src/io/sized.cr b/src/io/sized.cr
index 7c26b20319fa..ad451523fffe 100644
--- a/src/io/sized.cr
+++ b/src/io/sized.cr
@@ -29,7 +29,7 @@ class IO::Sized < IO
     check_open
 
     count = {slice.size.to_u64, @read_remaining}.min
-    bytes_read = @io.read slice[0, count]
+    bytes_read = @io.read(slice[0, count]).to_i32
     @read_remaining -= bytes_read
     bytes_read
   end
diff --git a/src/io/stapled.cr b/src/io/stapled.cr
index f236baf0ec76..98d90eadb238 100644
--- a/src/io/stapled.cr
+++ b/src/io/stapled.cr
@@ -33,7 +33,7 @@ class IO::Stapled < IO
   def read(slice : Bytes) : Int32
     check_open
 
-    @reader.read(slice)
+    @reader.read(slice).to_i32
   end
 
   # Gets a string from `reader`.
diff --git a/src/string.cr b/src/string.cr
index 953381d05221..a6c22706344c 100644
--- a/src/string.cr
+++ b/src/string.cr
@@ -817,7 +817,7 @@ class String
   # s[-2..-4] # => ""
   # s[-2..1]  # => ""
   # s[3..-4]  # => ""
-  # ``` : String
+  # ```
   def [](range : Range) : String
     self[*Indexable.range_to_index_and_count(range, size) || raise IndexError.new]
   end
@@ -5010,7 +5010,7 @@ class String
   # Raises an `ArgumentError` if `self` has null bytes. Returns `self` otherwise.
   #
   # This method should sometimes be called before passing a `String` to a C function.
-  def check_no_null_byte(name = nil) : String
+  def check_no_null_byte(name = nil) : self
     if byte_index(0)
       name = "`#{name}` " if name
       raise ArgumentError.new("String #{name}contains null byte")