diff --git a/history.textile b/history.textile
index 2227f1d2..fd82c0e0 100644
--- a/history.textile
+++ b/history.textile
@@ -1,3 +1,7 @@
+h2. Version 2.21.0
+
+* Fail plausible? if more than 1 + exists in a number.
+
 h2. Version 2.20.15
 
 * Pakistan (#531)
diff --git a/lib/phony/country_codes.rb b/lib/phony/country_codes.rb
index 0738d791..52be4c3d 100644
--- a/lib/phony/country_codes.rb
+++ b/lib/phony/country_codes.rb
@@ -94,6 +94,11 @@ def format(number, options = {})
     # Is this number plausible?
     #
     def plausible?(number, hints = {})
+      # Fail if it contains too many of certain phone specific markers:
+      #   * more than 1 +
+      #
+      return false if number.count('+') > 1
+
       normalized = clean number
 
       # False if it fails the basic check.
diff --git a/phony.gemspec b/phony.gemspec
index 9049537c..b4e4820c 100644
--- a/phony.gemspec
+++ b/phony.gemspec
@@ -1,6 +1,6 @@
 Gem::Specification.new do |s|
   s.name = 'phony'
-  s.version = '2.20.15'
+  s.version = '2.21.0'
   s.authors = ['Florian Hanke']
   s.email = 'florian.hanke+phony@gmail.com'
   s.homepage = 'https://github.com/floere/phony'
diff --git a/qed/plausibility.md b/qed/plausibility.md
index 992a7805..9978fd0d 100644
--- a/qed/plausibility.md
+++ b/qed/plausibility.md
@@ -41,6 +41,10 @@ The number is not considered plausible if it does not contain given `ccc`.
     Phony.refute.plausible?('+1 868 7620266', ccc: '1869')
     Phony.refute.plausible?('+1 869 7620266', ccc: '1868')
 
+### duplicated cc
+
+    Phony.refute.plausible?('+49+491505632832')
+
 ### Example countries
 
 Some of the examples use `plausible? true: [some numbers]`.