diff --git a/source/JSONSchema-Core-Tests/JSONSchemaTests.class.st b/source/JSONSchema-Core-Tests/JSONSchemaTests.class.st
index 4c111c8..44681d4 100644
--- a/source/JSONSchema-Core-Tests/JSONSchemaTests.class.st
+++ b/source/JSONSchema-Core-Tests/JSONSchemaTests.class.st
@@ -25,6 +25,40 @@ JSONSchemaTests >> testMultipleConstraintsOnAnyObject [
 		should: [ schema validate: '1234567' ] raise: JSONConstraintError
 ]
 
+{ #category : 'tests' }
+JSONSchemaTests >> testPatternPropertiesWithEscapedDotInCharacterClassIsSupported [
+	"Regression: the OAI OpenAPI-3.0 meta-schema uses [a-zA-Z0-9\.\-_]+ for component-name
+	patternProperties keys (components.schemas/responses/parameters/etc.) - Pharo's Regex
+	engine raised 'bad backslash escape' on the escaped dot inside the character class."
+	| schema |
+	schema := JSONSchema fromString: '{"type":"object","patternProperties":{"^[a-zA-Z0-9\\.\\-_]+$":{"type":"string"}},"additionalProperties":false}'.
+	self shouldnt: [ schema validate: {'Foo.Bar-1_2'->'ok'} asDictionary ] raise: Error.
+	self should: [ schema validate: {'has space'->'ok'} asDictionary ] raise: JSONSchemaError
+]
+
+{ #category : 'tests' }
+JSONSchemaTests >> testPatternPropertiesWithNonCapturingGroupIsSupported [
+	"Same regression as #testPatternWithNonCapturingGroupIsSupported, but for the
+	patternProperties keyword (matches property *names*, separate code path/call site)."
+	| schema |
+	schema := JSONSchema fromString: '{"type":"object","patternProperties":{"^[1-5](?:\\d{2}|XX)$":{"type":"string"}},"additionalProperties":false}'.
+	self shouldnt: [ schema validate: {'200'->'ok'} asDictionary ] raise: Error.
+	self shouldnt: [ schema validate: {'2XX'->'ok'} asDictionary ] raise: Error.
+	self should: [ schema validate: {'999'->'ok'} asDictionary ] raise: JSONSchemaError
+]
+
+{ #category : 'tests' }
+JSONSchemaTests >> testPatternWithNonCapturingGroupIsSupported [
+	"Regression: the OAI OpenAPI-3.0 meta-schema's Responses object uses the pattern
+	'^[1-5](?:\d{2}|XX)$' - Pharo's Regex engine used to raise 'Invalid lookaround
+	expression ?:' on the (?:...) syntax, crashing any validation that hit it."
+	| schema |
+	schema := JSONSchema fromString: '{"type":"string","pattern":"^[1-5](?:\\d{2}|XX)$"}'.
+	self shouldnt: [ schema validate: '200' ] raise: Error.
+	self shouldnt: [ schema validate: '2XX' ] raise: Error.
+	self should: [ schema validate: '999' ] raise: JSONConstraintError
+]
+
 { #category : 'tests' }
 JSONSchemaTests >> testSchemaReadArray [
 
diff --git a/source/JSONSchema-Core/JSONSchemaPatternConstraint.class.st b/source/JSONSchema-Core/JSONSchemaPatternConstraint.class.st
index d5c6016..c203b63 100644
--- a/source/JSONSchema-Core/JSONSchemaPatternConstraint.class.st
+++ b/source/JSONSchema-Core/JSONSchemaPatternConstraint.class.st
@@ -31,7 +31,7 @@ JSONSchemaPatternConstraint >> validate [
 
 { #category : 'validation' }
 JSONSchemaPatternConstraint >> validate: aString [
-	(pattern asRegex search: aString) ifFalse: [
+	(pattern asECMARegex search: aString) ifFalse: [
 		JSONConstraintError signal: aString, ' does not match pattern ', pattern ]
 ]
 
diff --git a/source/JSONSchema-Core/JSONSchemaPatternPropertiesConstraint.class.st b/source/JSONSchema-Core/JSONSchemaPatternPropertiesConstraint.class.st
index d245efe..341565e 100644
--- a/source/JSONSchema-Core/JSONSchemaPatternPropertiesConstraint.class.st
+++ b/source/JSONSchema-Core/JSONSchemaPatternPropertiesConstraint.class.st
@@ -36,7 +36,7 @@ JSONSchemaPatternPropertiesConstraint >> validate: aDictionary [
 	is Boolean true = accept all)."
 	| resolvedPatterns |
 	resolvedPatterns := patternProperties associations collect: [ :assoc |
-		{ assoc key asRegex. self resolveVisitor visitSchemaSpec: assoc value } ].
+		{ assoc key asECMARegex. self resolveVisitor visitSchemaSpec: assoc value } ].
 	aDictionary keysAndValuesDo: [ :key :value |
 		| matchedPattern |
 		matchedPattern := false.
diff --git a/source/JSONSchema-Core/String.extension.st b/source/JSONSchema-Core/String.extension.st
index 971baf5..7016c77 100644
--- a/source/JSONSchema-Core/String.extension.st
+++ b/source/JSONSchema-Core/String.extension.st
@@ -1,5 +1,34 @@
 Extension { #name : 'String' }
 
+{ #category : '*jsonschema-core' }
+String >> asECMARegex [
+	"Pharo's Regex engine doesn't accept some ECMA-262 syntax that real-world schemas use
+	(e.g. the OAI OpenAPI meta-schema), even though it is semantically equivalent for the
+	boolean match/no-match checks pattern/patternProperties need:
+	- non-capturing groups (?:...) - rewritten to a plain capturing group (...)
+	- an escaped literal dot \. inside a character class [...] - rewritten to a bare . (both
+	  mean 'literal dot' inside a class; Pharo's engine only accepts the unescaped form there)"
+	^ self asECMARegexSource asRegex
+]
+
+{ #category : '*jsonschema-core' }
+String >> asECMARegexSource [
+	"See #asECMARegex. Kept separate so the rewritten source itself is testable/inspectable."
+	| source result inClass i char |
+	source := self copyReplaceAll: '(?:' with: '('.
+	result := WriteStream on: String new.
+	i := 1.
+	inClass := false.
+	[ i <= source size ] whileTrue: [
+		char := source at: i.
+		(char == $[ and: [ inClass not ]) ifTrue: [ inClass := true ].
+		(char == $] and: [ inClass ]) ifTrue: [ inClass := false ].
+		(inClass and: [ char == $\ and: [ i < source size and: [ (source at: i + 1) == $. ] ] ])
+			ifTrue: [ result nextPut: $.. i := i + 2 ]
+			ifFalse: [ result nextPut: char. i := i + 1 ] ].
+	^ result contents
+]
+
 { #category : '*jsonschema-core' }
 String >> asJSONSchema [
 	^ JSONSchema string