diff --git a/spec/std/json/parser_spec.cr b/spec/std/json/parser_spec.cr
index 96cfd52277a2..7b8578f522c7 100644
--- a/spec/std/json/parser_spec.cr
+++ b/spec/std/json/parser_spec.cr
@@ -2,9 +2,13 @@ require "spec"
 require "json"
 
 private def it_parses(string, expected_value, file = __FILE__, line = __LINE__)
-  it "parses #{string}", file, line do
+  it "parses #{string} from String", file, line do
     JSON.parse(string).raw.should eq(expected_value)
   end
+
+  it "parses #{string} from IO", file, line do
+    JSON.parse(IO::Memory.new(string)).raw.should eq(expected_value)
+  end
 end
 
 private def it_raises_on_parse(string, file = __FILE__, line = __LINE__)
@@ -31,6 +35,7 @@ describe JSON::Parser do
   it_parses "[true]", [true]
   it_parses "[false]", [false]
   it_parses %(["hello"]), ["hello"]
+  it_parses %(["hello", 1]), ["hello", 1]
   it_parses "[0]", [0]
   it_parses " [ 0 ] ", [0]
 
diff --git a/spec/std/json/pull_parser_spec.cr b/spec/std/json/pull_parser_spec.cr
index 8de524e86c87..28ef4c6cf527 100644
--- a/spec/std/json/pull_parser_spec.cr
+++ b/spec/std/json/pull_parser_spec.cr
@@ -92,8 +92,8 @@ class JSON::PullParser
   end
 end
 
-private def assert_pull_parse(string)
-  it "parses #{string}" do
+private def assert_pull_parse(string, file = __FILE__, line = __LINE__)
+  it "parses #{string}", file, line do
     parser = JSON::PullParser.new string
     parser.assert JSON.parse(string).raw
     parser.kind.should eq(JSON::PullParser::Kind::EOF)
diff --git a/src/json/lexer.cr b/src/json/lexer.cr
index 3e61179b9844..067d595aeff3 100644
--- a/src/json/lexer.cr
+++ b/src/json/lexer.cr
@@ -220,8 +220,16 @@ abstract class JSON::Lexer
   private def consume_number
     number_start
 
+    # Integer values of up to 18 digits can be computed by doing math:
+    # no need to store a string value and later parse it.
+    # For larger numbers, or floats, we store the entire string and later parse it.
+    @token.int_value = nil
+    integer = 0_i64
+    negative = false
+
     if current_char == '-'
       append_number_char
+      negative = true
       next_char
     end
 
@@ -238,13 +246,19 @@ abstract class JSON::Lexer
         unexpected_char
       else
         @token.kind = :int
+        @token.int_value = 0
         number_end
       end
     when '1'..'9'
       append_number_char
+      digits = 1
+      integer = (current_char - '0').to_i64
       char = next_char
       while '0' <= char <= '9'
         append_number_char
+        digits += 1
+        integer &*= 10
+        integer &+= char - '0'
         char = next_char
       end
 
@@ -255,7 +269,13 @@ abstract class JSON::Lexer
         consume_exponent
       else
         @token.kind = :int
-        number_end
+        # Int64::MAX is 9223372036854775807 which has 19 digits.
+        # With 18 digits we know the number we computed is the one we read.
+        if digits > 18
+          number_end
+        else
+          @token.int_value = negative ? -integer : integer
+        end
       end
     else
       unexpected_char
diff --git a/src/json/lexer/io_based.cr b/src/json/lexer/io_based.cr
index d3989c54f0a8..f1f5346306db 100644
--- a/src/json/lexer/io_based.cr
+++ b/src/json/lexer/io_based.cr
@@ -2,17 +2,64 @@
 class JSON::Lexer::IOBased < JSON::Lexer
   def initialize(@io : IO)
     super()
-    @current_char = @io.read_char || '\0'
+    @current_char = @io.read_byte.try(&.chr) || '\0'
   end
 
   private getter current_char
 
   private def next_char_no_column_increment
-    @current_char = @io.read_char || '\0'
+    @current_char = @io.read_byte.try(&.chr) || '\0'
   end
 
   private def consume_string
-    consume_string_with_buffer
+    peek = @io.peek
+    if !peek || peek.empty?
+      return consume_string_with_buffer
+    end
+
+    pos = 0
+
+    while true
+      if pos >= peek.size
+        # We don't have enough data in the peek buffer to create a string:
+        # default to the slow method
+        return consume_string_with_buffer
+      end
+
+      char = peek[pos]
+      case char
+      when '\\'
+        # If we find an escape character, go to the slow method
+        @column_number += pos
+        return consume_string_at_escape_char(peek, pos)
+      when '"'
+        break
+      else
+        if 0 <= current_char.ord < 32
+          unexpected_char
+        else
+          pos += 1
+        end
+      end
+    end
+
+    @column_number += pos
+    @token.string_value =
+      if @expects_object_key
+        @string_pool.get(peek.to_unsafe, pos)
+      else
+        String.new(peek.to_unsafe, pos)
+      end
+
+    @io.skip(pos + 1)
+    next_char
+  end
+
+  private def consume_string_at_escape_char(peek, pos)
+    consume_string_with_buffer do
+      @buffer.write peek[0, pos]
+      @io.skip(pos)
+    end
   end
 
   private def number_start
diff --git a/src/json/lexer/string_based.cr b/src/json/lexer/string_based.cr
index 5696bc6f78b2..d8b3b64f1940 100644
--- a/src/json/lexer/string_based.cr
+++ b/src/json/lexer/string_based.cr
@@ -1,8 +1,9 @@
 # :nodoc:
 class JSON::Lexer::StringBased < JSON::Lexer
-  def initialize(string)
+  def initialize(string : String)
     super()
-    @reader = Char::Reader.new(string)
+    @string = string
+    @pos = 0
     @number_start = 0
   end
 
@@ -33,7 +34,7 @@ class JSON::Lexer::StringBased < JSON::Lexer
     if @expects_object_key
       start_pos += 1
       end_pos = current_pos - 1
-      @token.string_value = @string_pool.get(@reader.string.to_unsafe + start_pos, end_pos - start_pos)
+      @token.string_value = @string_pool.get(@string.to_unsafe + start_pos, end_pos - start_pos)
     else
       @token.string_value = string_range(start_pos + 1, current_pos - 1)
     end
@@ -47,27 +48,30 @@ class JSON::Lexer::StringBased < JSON::Lexer
   end
 
   private def current_pos
-    @reader.pos
+    @pos
   end
 
   def string_range(start_pos, end_pos) : String
-    @reader.string.byte_slice(start_pos, end_pos - start_pos)
+    @string.byte_slice(start_pos, end_pos - start_pos)
   end
 
   def slice_range(start_pos, end_pos) : Bytes
-    @reader.string.to_slice[start_pos, end_pos - start_pos]
+    @string.to_slice[start_pos, end_pos - start_pos]
   end
 
   private def next_char_no_column_increment
-    char = @reader.next_char
-    if char == '\0' && @reader.pos != @reader.string.bytesize
+    @pos += 1
+
+    char = current_char
+    if char == '\0' && @pos != @string.bytesize
       unexpected_char
     end
+
     char
   end
 
   private def current_char
-    @reader.current_char
+    @string.to_unsafe[@pos].chr
   end
 
   private def number_start
diff --git a/src/json/token.cr b/src/json/token.cr
index 436709aec233..f1862ce676f5 100644
--- a/src/json/token.cr
+++ b/src/json/token.cr
@@ -19,7 +19,7 @@ class JSON::Token
   property string_value : String
 
   def int_value : Int64
-    raw_value.to_i64
+    @int_value || raw_value.to_i64
   rescue exc : ArgumentError
     raise ParseException.new(exc.message, line_number, column_number)
   end
@@ -32,7 +32,8 @@ class JSON::Token
 
   property line_number : Int32
   property column_number : Int32
-  property raw_value : String
+  setter raw_value : String
+  setter int_value : Int64?
 
   def initialize
     @kind = :EOF
@@ -40,6 +41,16 @@ class JSON::Token
     @column_number = 0
     @string_value = ""
     @raw_value = ""
+    @int_value = nil
+  end
+
+  def raw_value
+    case @kind
+    when .int?
+      @int_value.try(&.to_s) || @raw_value
+    else
+      @raw_value
+    end
   end
 
   def to_s(io : IO) : Nil
@@ -51,7 +62,11 @@ class JSON::Token
     when .true?
       io << "true"
     when .int?
-      raw_value.to_s(io)
+      if int_value = @int_value
+        int_value.to_s(io)
+      else
+        raw_value.to_s(io)
+      end
     when .float?
       raw_value.to_s(io)
     when .string?