diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 6d663552433..1edac7e57db 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -76,6 +76,9 @@ Bug Fixes
   wrong default AttributeFactory for new Tokenizers.
   (Terry Smith, Uwe Schindler)
 
+* LUCENE-7389: Fix FieldType.setDimensions(...) validation for the dimensionNumBytes
+  parameter. (Martijn van Groningen)
+
 Improvements
 
 * LUCENE-7323: Compound file writing now verifies the incoming
diff --git a/lucene/core/src/java/org/apache/lucene/document/FieldType.java b/lucene/core/src/java/org/apache/lucene/document/FieldType.java
index 2c0a62cbce3..e0f058f520e 100644
--- a/lucene/core/src/java/org/apache/lucene/document/FieldType.java
+++ b/lucene/core/src/java/org/apache/lucene/document/FieldType.java
@@ -374,7 +374,7 @@ public class FieldType implements IndexableFieldType  {
     if (dimensionNumBytes < 0) {
       throw new IllegalArgumentException("dimensionNumBytes must be >= 0; got " + dimensionNumBytes);
     }
-    if (dimensionCount > PointValues.MAX_NUM_BYTES) {
+    if (dimensionNumBytes > PointValues.MAX_NUM_BYTES) {
       throw new IllegalArgumentException("dimensionNumBytes must be <= " + PointValues.MAX_NUM_BYTES + "; got " + dimensionNumBytes);
     }
     if (dimensionCount == 0) {
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestPointValues.java b/lucene/core/src/test/org/apache/lucene/index/TestPointValues.java
index 9693c5c32b1..a846c276fef 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestPointValues.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestPointValues.java
@@ -362,9 +362,8 @@ public class TestPointValues extends LuceneTestCase {
     IndexWriterConfig iwc = new IndexWriterConfig(new MockAnalyzer(random()));
     IndexWriter w = new IndexWriter(dir, iwc);
     Document doc = new Document();
-    doc.add(new BinaryPoint("dim", new byte[PointValues.MAX_NUM_BYTES+1]));
     expectThrows(IllegalArgumentException.class, () -> {
-      w.addDocument(doc);
+      doc.add(new BinaryPoint("dim", new byte[PointValues.MAX_NUM_BYTES+1]));
     });
 
     Document doc2 = new Document();