diff --git a/lib/gitlab/ci/pipeline/expression.rb b/lib/gitlab/ci/pipeline/expression.rb
new file mode 100644
index 00000000000..f57df7c5637
--- /dev/null
+++ b/lib/gitlab/ci/pipeline/expression.rb
@@ -0,0 +1,10 @@
+module Gitlab
+  module Ci
+    module Pipeline
+      module Expression
+        ExpressionError = Class.new(StandardError)
+        RuntimeError = Class.new(ExpressionError)
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/ci/pipeline/expression/lexeme/pattern.rb b/lib/gitlab/ci/pipeline/expression/lexeme/pattern.rb
index 2ff527e34a8..59b8e4fad4c 100644
--- a/lib/gitlab/ci/pipeline/expression/lexeme/pattern.rb
+++ b/lib/gitlab/ci/pipeline/expression/lexeme/pattern.rb
@@ -11,10 +11,9 @@ module Gitlab
             end
 
             def evaluate(variables = {})
-              # TODO multiline support
               @regexp = Gitlab::UntrustedRegexp.new(@value)
             rescue RegexpError
-              raise Parser::ParserError, 'Invalid regular expression!'
+              raise Expression::RuntimeError, 'Invalid regular expression!'
             end
 
             def self.build(string)
diff --git a/lib/gitlab/ci/pipeline/expression/lexer.rb b/lib/gitlab/ci/pipeline/expression/lexer.rb
index e1c68b7c3c2..ebc6565266f 100644
--- a/lib/gitlab/ci/pipeline/expression/lexer.rb
+++ b/lib/gitlab/ci/pipeline/expression/lexer.rb
@@ -5,6 +5,8 @@ module Gitlab
         class Lexer
           include ::Gitlab::Utils::StrongMemoize
 
+          SyntaxError = Class.new(Expression::ExpressionError)
+
           LEXEMES = [
             Expression::Lexeme::Variable,
             Expression::Lexeme::String,
@@ -12,8 +14,6 @@ module Gitlab
             Expression::Lexeme::Equals
           ].freeze
 
-          SyntaxError = Class.new(Statement::StatementError)
-
           MAX_TOKENS = 100
 
           def initialize(statement, max_tokens: MAX_TOKENS)
diff --git a/lib/gitlab/ci/pipeline/expression/parser.rb b/lib/gitlab/ci/pipeline/expression/parser.rb
index fe23ab0b2f8..90f94d0b763 100644
--- a/lib/gitlab/ci/pipeline/expression/parser.rb
+++ b/lib/gitlab/ci/pipeline/expression/parser.rb
@@ -3,8 +3,6 @@ module Gitlab
     module Pipeline
       module Expression
         class Parser
-          ParserError = Class.new(Statement::StatementError)
-
           def initialize(tokens)
             @tokens = tokens.to_enum
             @nodes = []
diff --git a/lib/gitlab/ci/pipeline/expression/statement.rb b/lib/gitlab/ci/pipeline/expression/statement.rb
index 363e0b708a6..de37c50d2a2 100644
--- a/lib/gitlab/ci/pipeline/expression/statement.rb
+++ b/lib/gitlab/ci/pipeline/expression/statement.rb
@@ -3,7 +3,7 @@ module Gitlab
     module Pipeline
       module Expression
         class Statement
-          StatementError = Class.new(StandardError)
+          StatementError = Class.new(Expression::ExpressionError)
 
           GRAMMAR = [
             %w[variable equals string],
@@ -35,13 +35,13 @@ module Gitlab
 
           def truthful?
             evaluate.present?
-          rescue StatementError
+          rescue Expression::ExpressionError
             false
           end
 
           def valid?
             parse_tree.is_a?(Lexeme::Base)
-          rescue StatementError
+          rescue Expression::ExpressionError
             false
           end
         end
diff --git a/spec/lib/gitlab/ci/pipeline/expression/lexeme/pattern_spec.rb b/spec/lib/gitlab/ci/pipeline/expression/lexeme/pattern_spec.rb
index ed69742cd7c..47385ce0a5b 100644
--- a/spec/lib/gitlab/ci/pipeline/expression/lexeme/pattern_spec.rb
+++ b/spec/lib/gitlab/ci/pipeline/expression/lexeme/pattern_spec.rb
@@ -56,7 +56,7 @@ describe Gitlab::Ci::Pipeline::Expression::Lexeme::Pattern do
       regexp = described_class.new('invalid ( .*')
 
       expect { regexp.evaluate }
-        .to raise_error(Gitlab::Ci::Pipeline::Expression::Parser::ParserError)
+        .to raise_error(Gitlab::Ci::Pipeline::Expression::RuntimeError)
     end
   end
 end
diff --git a/spec/lib/gitlab/ci/pipeline/expression/lexer_spec.rb b/spec/lib/gitlab/ci/pipeline/expression/lexer_spec.rb
index 230ceeb07f8..3f11b3f7673 100644
--- a/spec/lib/gitlab/ci/pipeline/expression/lexer_spec.rb
+++ b/spec/lib/gitlab/ci/pipeline/expression/lexer_spec.rb
@@ -6,7 +6,7 @@ describe Gitlab::Ci::Pipeline::Expression::Lexer do
   end
 
   describe '#tokens' do
-    it 'tokenss single value' do
+    it 'returns single value' do
       tokens = described_class.new('$VARIABLE').tokens
 
       expect(tokens).to be_one
@@ -20,14 +20,14 @@ describe Gitlab::Ci::Pipeline::Expression::Lexer do
       expect(tokens).to all(be_an_instance_of(token_class))
     end
 
-    it 'tokenss multiple values of the same token' do
+    it 'returns multiple values of the same token' do
       tokens = described_class.new("$VARIABLE1 $VARIABLE2").tokens
 
       expect(tokens.size).to eq 2
       expect(tokens).to all(be_an_instance_of(token_class))
     end
 
-    it 'tokenss multiple values with different tokens' do
+    it 'returns multiple values with different tokens' do
       tokens = described_class.new('$VARIABLE "text" "value"').tokens
 
       expect(tokens.size).to eq 3
@@ -36,7 +36,7 @@ describe Gitlab::Ci::Pipeline::Expression::Lexer do
       expect(tokens.third.value).to eq '"value"'
     end
 
-    it 'tokenss tokens and operators' do
+    it 'returns tokens and operators' do
       tokens = described_class.new('$VARIABLE == "text"').tokens
 
       expect(tokens.size).to eq 3
diff --git a/spec/lib/gitlab/ci/pipeline/expression/statement_spec.rb b/spec/lib/gitlab/ci/pipeline/expression/statement_spec.rb
index 633c932eabb..6d58838bf14 100644
--- a/spec/lib/gitlab/ci/pipeline/expression/statement_spec.rb
+++ b/spec/lib/gitlab/ci/pipeline/expression/statement_spec.rb
@@ -36,7 +36,7 @@ describe Gitlab::Ci::Pipeline::Expression::Statement do
         '== "123"',      # invalid left side
         '"some string"', # only string provided
         '$VAR ==',       # invalid right side
-        '12345',         # unknown syntax
+        'null',          # missing lexemes
         ''               # empty statement
       ]
 
@@ -44,7 +44,7 @@ describe Gitlab::Ci::Pipeline::Expression::Statement do
         context "when expression grammar is #{syntax.inspect}" do
           let(:text) { syntax }
 
-          it 'aises a statement error exception' do
+          it 'raises a statement error exception' do
             expect { subject.parse_tree }
               .to raise_error described_class::StatementError
           end