diff --git a/spec/std/random/system_spec.cr b/spec/std/random/system_spec.cr
new file mode 100644
index 000000000000..ee55adeddbf5
--- /dev/null
+++ b/spec/std/random/system_spec.cr
@@ -0,0 +1,16 @@
+require "spec"
+require "random/system"
+
+describe "Random::System" do
+  rng = Random::System.new
+
+  it "returns random number from the secure system source" do
+    rng.next_u.should be_a(Int::Unsigned)
+
+    x = rng.rand(123456...654321)
+    x.should be >= 123456
+    x.should be < 654321
+
+    rng.rand(Int64::MAX / 2).should be <= (Int64::MAX / 2)
+  end
+end
diff --git a/src/compiler/crystal/semantic/flags.cr b/src/compiler/crystal/semantic/flags.cr
index 0481644bc7ba..a2d0fa2a71cd 100644
--- a/src/compiler/crystal/semantic/flags.cr
+++ b/src/compiler/crystal/semantic/flags.cr
@@ -26,6 +26,8 @@ class Crystal::Program
     set.add "darwin" if set.any?(&.starts_with?("macosx")) || set.any?(&.starts_with?("darwin"))
     set.add "freebsd" if set.any?(&.starts_with?("freebsd"))
     set.add "openbsd" if set.any?(&.starts_with?("openbsd"))
+    set.add "unix" if set.any? { |flag| %w(cygnus darwin freebsd linux openbsd).includes?(flag) }
+
     set.add "x86_64" if set.any?(&.starts_with?("amd64"))
     set.add "i686" if set.any? { |flag| %w(i586 i486 i386).includes?(flag) }
 
diff --git a/src/crystal/system/random.cr b/src/crystal/system/random.cr
new file mode 100644
index 000000000000..881c26cac462
--- /dev/null
+++ b/src/crystal/system/random.cr
@@ -0,0 +1,27 @@
+# :nodoc:
+module Crystal
+  # :nodoc:
+  module System
+    # :nodoc:
+    module Random
+      # Fills *buffer* with random bytes from a secure source.
+      # def self.random_bytes(buffer : Bytes) : Nil
+
+      # Returns a random unsigned integer from a secure source. Implementations
+      # may choose the integer size to return based on what the system source
+      # provides. They may choose to return a single byte (UInt8) in which case
+      # `::Random` will prefer `#random_bytes` to read as many bytes as required
+      # at once, avoiding multiple reads or reading too many bytes.
+      # def self.next_u
+    end
+  end
+end
+
+{% if flag?(:linux) %}
+  require "./unix/getrandom"
+{% elsif flag?(:openbsd) %}
+  require "./unix/arc4random"
+{% else %}
+  # TODO: restrict on flag?(:unix) after crystal > 0.22.0 is released
+  require "./unix/urandom"
+{% end %}
diff --git a/src/crystal/system/unix/arc4random.cr b/src/crystal/system/unix/arc4random.cr
new file mode 100644
index 000000000000..67aa0867560a
--- /dev/null
+++ b/src/crystal/system/unix/arc4random.cr
@@ -0,0 +1,16 @@
+{% skip_file unless flag?(:openbsd) %}
+
+require "c/stdlib"
+
+module Crystal::System::Random
+  # Fills *buffer* with random bytes using arc4random.
+  #
+  # NOTE: only secure on OpenBSD and CloudABI
+  def self.random_bytes(buffer : Bytes) : Nil
+    LibC.arc4random_buf(buffer.to_unsafe.as(Void*), buffer.size)
+  end
+
+  def self.next_u : UInt32
+    LibC.arc4random
+  end
+end
diff --git a/src/crystal/system/unix/getrandom.cr b/src/crystal/system/unix/getrandom.cr
new file mode 100644
index 000000000000..68ae5035a0e9
--- /dev/null
+++ b/src/crystal/system/unix/getrandom.cr
@@ -0,0 +1,84 @@
+{% skip_file unless flag?(:linux) %}
+
+require "c/unistd"
+require "c/sys/syscall"
+
+module Crystal::System::Random
+  @@initialized = false
+  @@getrandom_available = false
+
+  private def self.init
+    @@initialized = true
+
+    if sys_getrandom(Bytes.new(16)) >= 0
+      @@getrandom_available = true
+    else
+      @@urandom = urandom = File.open("/dev/urandom", "r")
+      urandom.sync = true # don't buffer bytes
+    end
+  end
+
+  # Reads n random bytes using the Linux `getrandom(2)` syscall.
+  def self.random_bytes(buf : Bytes) : Nil
+    init unless @@initialized
+
+    if @@getrandom_available
+      getrandom(buf)
+    elsif urandom = @@urandom
+      urandom.read_fully(buf)
+    else
+      raise "Failed to access secure source to generate random bytes!"
+    end
+  end
+
+  def self.next_u : UInt8
+    init unless @@initialized
+
+    if @@getrandom_available
+      buf = uninitialized UInt8[1]
+      getrandom(buf.to_slice)
+      buf.to_unsafe.as(UInt8*).value
+    elsif urandom = @@urandom
+      urandom.read_byte.not_nil!
+    else
+      raise "Failed to access secure source to generate random bytes!"
+    end
+  end
+
+  # Reads n random bytes using the Linux `getrandom(2)` syscall.
+  private def self.getrandom(buf)
+    # getrandom(2) may only read up to 256 bytes at once without being
+    # interrupted or returning early
+    chunk_size = 256
+
+    while buf.size > 0
+      if buf.size < chunk_size
+        chunk_size = buf.size
+      end
+
+      read_bytes = sys_getrandom(buf[0, chunk_size])
+      raise Errno.new("getrandom") if read_bytes == -1
+
+      buf += read_bytes
+    end
+  end
+
+  # Low-level wrapper for the `getrandom(2)` syscall, returns the number of
+  # bytes read or `-1` if an error occured (or the syscall isn't available)
+  # and sets `Errno.value`.
+  #
+  # We use the kernel syscall instead of the `getrandom` C function so any
+  # binary compiled for Linux will always use getrandom if the kernel is 3.17+
+  # and silently fallback to read from /dev/urandom if not (so it's more
+  # portable).
+  private def self.sys_getrandom(buf : Bytes)
+    loop do
+      read_bytes = LibC.syscall(LibC::SYS_getrandom, buf, LibC::SizeT.new(buf.size), 0)
+      if read_bytes < 0 && (Errno.value == Errno::EINTR || Errno.value == Errno::EAGAIN)
+        Fiber.yield
+      else
+        return read_bytes
+      end
+    end
+  end
+end
diff --git a/src/crystal/system/unix/urandom.cr b/src/crystal/system/unix/urandom.cr
new file mode 100644
index 000000000000..d42612dfa0b6
--- /dev/null
+++ b/src/crystal/system/unix/urandom.cr
@@ -0,0 +1,32 @@
+# TODO: replace with `flag?(:unix) && !flag?(:openbsd) && !flag?(:linux)` after crystal > 0.22.0 is released
+{% skip_file if flag?(:openbsd) && flag?(:linux) %}
+
+module Crystal::System::Random
+  @@initialized = false
+
+  private def self.init
+    @@initialized = true
+    @@urandom = urandom = File.open("/dev/urandom", "r")
+    urandom.sync = true # don't buffer bytes
+  end
+
+  def self.random_bytes(buf : Bytes) : Nil
+    init unless @@initialized
+
+    if urandom = @@urandom
+      urandom.read_fully(buf)
+    else
+      raise "Failed to access secure source to generate random bytes!"
+    end
+  end
+
+  def self.next_u : UInt8
+    init unless @@initialized
+
+    if urandom = @@urandom
+      urandom.read_bytes(UInt8)
+    else
+      raise "Failed to access secure source to generate random bytes!"
+    end
+  end
+end
diff --git a/src/lib_c/amd64-unknown-openbsd/c/stdlib.cr b/src/lib_c/amd64-unknown-openbsd/c/stdlib.cr
index 5729203618e5..079cee258a8b 100644
--- a/src/lib_c/amd64-unknown-openbsd/c/stdlib.cr
+++ b/src/lib_c/amd64-unknown-openbsd/c/stdlib.cr
@@ -7,6 +7,8 @@ lib LibC
     rem : Int
   end
 
+  fun arc4random : UInt32
+  fun arc4random_buf(x0 : Void*, x1 : SizeT) : Void
   fun atof(x0 : Char*) : Double
   fun div(x0 : Int, x1 : Int) : DivT
   fun exit(x0 : Int) : NoReturn
diff --git a/src/random.cr b/src/random.cr
index 2086a1a5ec70..1319ef4c9697 100644
--- a/src/random.cr
+++ b/src/random.cr
@@ -194,12 +194,7 @@ module Random
             end
 
           loop do
-            # Build up the number combining multiple outputs from the RNG.
-            result = {{utype}}.new(next_u)
-            (needed_parts - 1).times do
-              result <<= sizeof(typeof(next_u))*8
-              result |= {{utype}}.new(next_u)
-            end
+            result = rand_type({{utype}}, needed_parts)
 
             # For a uniform distribution we may need to throw away some numbers.
             if result < limit || limit == 0
@@ -228,9 +223,7 @@ module Random
       end
 
       # Generates a random integer in range `{{type}}::MIN..{{type}}::MAX`.
-      private def rand_type(type : {{type}}.class) : {{type}}
-        needed_parts = {{size/8}} / sizeof(typeof(next_u))
-
+      private def rand_type(type : {{type}}.class, needed_parts = sizeof({{type}}) / sizeof(typeof(next_u))) : {{type}}
         # Build up the number combining multiple outputs from the RNG.
         result = {{utype}}.new(next_u)
         (needed_parts - 1).times do
diff --git a/src/random/system.cr b/src/random/system.cr
new file mode 100644
index 000000000000..1c81cda9def0
--- /dev/null
+++ b/src/random/system.cr
@@ -0,0 +1,52 @@
+require "crystal/system/random"
+
+# Generates random numbers from a secure source of the system.
+#
+# For example `arc4random` is used on OpenBSD, whereas on Linux it uses
+# `getrandom` (if the kernel supports it) and fallbacks on reading from
+# `/dev/urandom` on UNIX systems.
+struct Random::System
+  include Random
+
+  def initialize
+  end
+
+  def next_u
+    Crystal::System::Random.next_u
+  end
+
+  {% for type in [UInt8, UInt16, UInt32, UInt64] %}
+    # Generates a random integer of a given type. The number of bytes to
+    # generate can be limited; by default it will generate as many bytes as
+    # needed to fill the integer size.
+    private def rand_type(type : {{type}}.class, needed_parts = nil) : {{type}}
+      needed_bytes =
+        if needed_parts
+          needed_parts * sizeof(typeof(next_u))
+        else
+          sizeof({{type}})
+        end
+
+      buf = uninitialized UInt8[sizeof({{type}})]
+
+      if needed_bytes < sizeof({{type}})
+        bytes = Slice.new(buf.to_unsafe, needed_bytes)
+        Crystal::System::Random.random_bytes(bytes)
+
+        bytes.reduce({{type}}.new(0)) do |result, byte|
+          (result << 8) | byte
+        end
+      else
+        Crystal::System::Random.random_bytes(buf.to_slice)
+        buf.to_unsafe.as({{type}}*).value
+      end
+    end
+  {% end %}
+
+  {% for type in [Int8, Int16, Int32, Int64] %}
+    private def rand_type(type : {{type}}.class, needed_bytes = sizeof({{type}})) : {{type}}
+      result = rand_type({{"U#{type}".id}}, needed_bytes)
+      {{type}}.new(result)
+    end
+  {% end %}
+end
diff --git a/src/secure_random.cr b/src/secure_random.cr
index 5828c4044cde..d713f1a95a38 100644
--- a/src/secure_random.cr
+++ b/src/secure_random.cr
@@ -1,9 +1,5 @@
 require "base64"
-
-{% if flag?(:linux) %}
-  require "c/unistd"
-  require "c/sys/syscall"
-{% end %}
+require "crystal/system/random"
 
 # The `SecureRandom` module is an interface for creating cryptography secure
 # random values in different formats.
@@ -20,8 +16,6 @@ require "base64"
 # implementation and uses `getrandom` on Linux (when provided by the kernel),
 # then tries to read from `/dev/urandom`.
 module SecureRandom
-  @@initialized = false
-
   # Generates *n* random bytes that are encoded into base64.
   #
   # Check `Base64#strict_encode` for details.
@@ -80,78 +74,9 @@ module SecureRandom
   # slice                            # => [217, 118, 38, 196]
   # ```
   def self.random_bytes(buf : Bytes) : Nil
-    init unless @@initialized
-
-    {% if flag?(:linux) %}
-      if @@getrandom_available
-        getrandom(buf)
-        return
-      end
-    {% end %}
-
-    if urandom = @@urandom
-      urandom.read_fully(buf)
-      return
-    end
-
-    raise "Failed to access secure source to generate random bytes!"
-  end
-
-  private def self.init
-    @@initialized = true
-
-    {% if flag?(:linux) %}
-      if sys_getrandom(Bytes.new(16)) >= 0
-        @@getrandom_available = true
-        return
-      end
-    {% end %}
-
-    @@urandom = urandom = File.open("/dev/urandom", "r")
-    urandom.sync = true # don't buffer bytes
+    Crystal::System::Random.random_bytes(buf)
   end
 
-  {% if flag?(:linux) %}
-    @@getrandom_available = false
-
-    # Reads n random bytes using the Linux `getrandom(2)` syscall.
-    private def self.getrandom(buf : Bytes)
-      # getrandom(2) may only read up to 256 bytes at once without being
-      # interrupted or returning early
-      chunk_size = 256
-
-      while buf.size > 0
-        if buf.size < chunk_size
-          chunk_size = buf.size
-        end
-
-        read_bytes = sys_getrandom(buf[0, chunk_size])
-        raise Errno.new("getrandom") if read_bytes == -1
-
-        buf += read_bytes
-      end
-    end
-
-    # Low-level wrapper for the `getrandom(2)` syscall, returns the number of
-    # bytes read or `-1` if an error occured (or the syscall isn't available)
-    # and sets `Errno.value`.
-    #
-    # We use the kernel syscall instead of the `getrandom` C function so any
-    # binary compiled for Linux will always use getrandom if the kernel is 3.17+
-    # and silently fallback to read from /dev/urandom if not (so it's more
-    # portable).
-    private def self.sys_getrandom(buf : Bytes)
-      loop do
-        read_bytes = LibC.syscall(LibC::SYS_getrandom, buf, LibC::SizeT.new(buf.size), 0)
-        if read_bytes < 0 && (Errno.value == Errno::EINTR || Errno.value == Errno::EAGAIN)
-          Fiber.yield
-        else
-          return read_bytes
-        end
-      end
-    end
-  {% end %}
-
   # Generates a UUID (Universally Unique Identifier).
   #
   # It generates a random v4 UUID. Check [RFC 4122 Section 4.4](https://tools.ietf.org/html/rfc4122#section-4.4)