diff --git a/src/main/kotlin/com/github/erosb/jsonsKema/JsonParser.kt b/src/main/kotlin/com/github/erosb/jsonsKema/JsonParser.kt
index 647dbf7..fc03d22 100644
--- a/src/main/kotlin/com/github/erosb/jsonsKema/JsonParser.kt
+++ b/src/main/kotlin/com/github/erosb/jsonsKema/JsonParser.kt
@@ -186,6 +186,12 @@ class JsonParser private constructor(
                 walker.skipWhitespaces().consume(":").skipWhitespaces()
                 val propValue = parseValue()
                 nestingPath.removeLast()
+                if (properties.keys.contains(propName)) {
+                    throw DuplicateObjectPropertyException(
+                        properties.keys.find { it.value == propName.value }!!,
+                        propName
+                    )
+                }
                 properties.put(propName, propValue)
                 if (walker.curr() == ',') {
                     commaCharFound = true
diff --git a/src/main/kotlin/com/github/erosb/jsonsKema/JsonValue.kt b/src/main/kotlin/com/github/erosb/jsonsKema/JsonValue.kt
index c42cd5b..6c7faff 100644
--- a/src/main/kotlin/com/github/erosb/jsonsKema/JsonValue.kt
+++ b/src/main/kotlin/com/github/erosb/jsonsKema/JsonValue.kt
@@ -6,7 +6,12 @@ import java.math.BigDecimal
 import java.net.URI
 import java.util.stream.Collectors.joining
 
-data class JsonParseException(override val message: String, val location: TextLocation) : RuntimeException()
+open class JsonParseException(override val message: String, val location: TextLocation) : RuntimeException()
+
+class DuplicateObjectPropertyException(
+    firstOccurrence: JsonString,
+    secondOccurrence: JsonString
+): JsonParseException("property \"${firstOccurrence.value}\" found at multiple locations in the same object, ${firstOccurrence.location} and ${secondOccurrence.location}", secondOccurrence.location)
 
 data class JsonTypingException(
     val expectedType: String,
diff --git a/src/test/kotlin/com/github/erosb/jsonsKema/JsonParserTest.kt b/src/test/kotlin/com/github/erosb/jsonsKema/JsonParserTest.kt
index 56152c4..d2accc6 100644
--- a/src/test/kotlin/com/github/erosb/jsonsKema/JsonParserTest.kt
+++ b/src/test/kotlin/com/github/erosb/jsonsKema/JsonParserTest.kt
@@ -105,7 +105,8 @@ class JsonParserTest {
         val exception = assertThrows(JsonParseException::class.java) {
             JsonParser("nil")()
         }
-        assertEquals(JsonParseException("Unexpected character found: i", TextLocation(1, 2, DEFAULT_BASE_URI)), exception)
+        assertEquals("Unexpected character found: i", exception.message)
+        assertEquals(TextLocation(1, 2, DEFAULT_BASE_URI), exception.location)
     }
 
     @Test
@@ -113,7 +114,8 @@ class JsonParserTest {
         val exception = assertThrows(JsonParseException::class.java) {
             JsonParser("nu")()
         }
-        assertEquals(JsonParseException("Unexpected EOF", TextLocation(1, 3, DEFAULT_BASE_URI)), exception)
+        assertEquals("Unexpected EOF", exception.message)
+        assertEquals(TextLocation(1, 3, DEFAULT_BASE_URI), exception.location)
     }
 
     @Test
@@ -121,7 +123,8 @@ class JsonParserTest {
         val exception = assertThrows(JsonParseException::class.java) {
             JsonParser("")()
         }
-        assertEquals(JsonParseException("Unexpected EOF", TextLocation(1, 1, DEFAULT_BASE_URI)), exception)
+        assertEquals("Unexpected EOF", exception.message)
+        assertEquals(TextLocation(1, 1, DEFAULT_BASE_URI), exception.location)
     }
 
     @Test
@@ -129,7 +132,8 @@ class JsonParserTest {
         val exception = assertThrows(JsonParseException::class.java) {
             JsonParser("{\"key1\":\"value1\", \"key2\":\"value2\" \"key3\":\"value3\"}\n")()
         }
-        assertEquals(JsonParseException("Unexpected character found: \". Expected ',', '}'", SourceLocation(1, 35, pointer())), exception)
+        assertEquals("Unexpected character found: \". Expected ',', '}'", exception.message)
+        assertEquals(SourceLocation(1, 35, pointer()), exception.location)
     }
 
     @Test
@@ -137,7 +141,8 @@ class JsonParserTest {
         val exception = assertThrows(JsonParseException::class.java) {
             JsonParser("[1, 2 3]")()
         }
-        assertEquals(JsonParseException("Unexpected character found: 3. Expected ',', ']'", SourceLocation(1, 7, pointer())), exception)
+        assertEquals("Unexpected character found: 3. Expected ',', ']'", exception.message)
+        assertEquals(SourceLocation(1, 7, pointer()), exception.location)
     }
 
     @Test
@@ -168,7 +173,8 @@ class JsonParserTest {
             val exception = assertThrows(JsonParseException::class.java) {
                 JsonParser("\"p\\u022suffix\"")()
             }
-            assertEquals(JsonParseException("invalid unicode sequence: 022s", TextLocation(1, 4, DEFAULT_BASE_URI)), exception)
+            assertEquals("invalid unicode sequence: 022s", exception.message)
+            assertEquals(TextLocation(1, 4, DEFAULT_BASE_URI), exception.location)
         }
 
         @Test
@@ -176,7 +182,8 @@ class JsonParserTest {
             val exception = assertThrows(JsonParseException::class.java) {
                 JsonParser("\"p\\u022")()
             }
-            assertEquals(JsonParseException("Unexpected EOF", TextLocation(1, 8, DEFAULT_BASE_URI)), exception)
+            assertEquals("Unexpected EOF", exception.message)
+            assertEquals(TextLocation(1, 8, DEFAULT_BASE_URI), exception.location)
         }
 
         @Test
@@ -191,7 +198,8 @@ class JsonParserTest {
         val exception = assertThrows(JsonParseException::class.java) {
             JsonParser("\r\n  \"")()
         }
-        assertEquals(JsonParseException("Unexpected EOF", SourceLocation(2, 4, pointer())), exception)
+        assertEquals("Unexpected EOF", exception.message)
+        assertEquals(SourceLocation(2, 4, pointer()), exception.location)
     }
 
     @Test
@@ -378,4 +386,40 @@ class JsonParserTest {
             .ignoringFieldsOfTypes(SourceLocation::class.java)
             .isEqualTo(expected)
     }
+
+    @Test
+    fun `duplicate key causes exception`() {
+        assertThrows(JsonParseException::class.java) {
+            JsonParser(
+                """
+            {
+                "a": 2,
+                "b": 2,
+                "a": 3
+            }
+        """.trimIndent()
+            )()
+        }
+    }
+
+    @Test
+    fun `duplicate key check works only on same nesting level`() {
+            JsonParser(
+                """
+            {
+                "a": {
+                    "a": 2,
+                    "b": [ "a" ]
+                },
+                "b": 2,
+                "c": [
+                    "a",
+                    {"a": false},
+                    "a",
+                    [ "a" ]
+                ]
+            }
+        """.trimIndent()
+            )()
+    }
 }