diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index bc5fd58775d1..9fd20d0b5111 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -76,6 +76,8 @@ Bug Fixes
   returns a string which can be parsed back into the original node.
   (Peter Barna, Adam Schwartz)
 
+* GITHUB#15133: Take the FST suffix cache into account when reporting FST ramBytesUsed (Anh Dung Bui)
+
 * GITHUB#14847: Allow Faiss vector format to index >2GB of vectors per-field per-segment by using MemorySegment APIs
   (instead of ByteBuffer) to copy bytes to native memory. (Kaival Parikh)
 
diff --git a/lucene/core/src/java/org/apache/lucene/util/fst/FSTCompiler.java b/lucene/core/src/java/org/apache/lucene/util/fst/FSTCompiler.java
index 43a3bfc62631..b99a80d09c92 100644
--- a/lucene/core/src/java/org/apache/lucene/util/fst/FSTCompiler.java
+++ b/lucene/core/src/java/org/apache/lucene/util/fst/FSTCompiler.java
@@ -1038,6 +1038,9 @@ public long fstRamBytesUsed() {
     if (dataOutput instanceof Accountable) {
       ramBytesUsed += ((Accountable) dataOutput).ramBytesUsed();
     }
+    if (suffixDedupCache != null) {
+      ramBytesUsed += suffixDedupCache.ramBytesUsed();
+    }
     return ramBytesUsed;
   }
 
diff --git a/lucene/core/src/java/org/apache/lucene/util/fst/FSTSuffixNodeCache.java b/lucene/core/src/java/org/apache/lucene/util/fst/FSTSuffixNodeCache.java
index f33f09e90723..8171dbd26c18 100644
--- a/lucene/core/src/java/org/apache/lucene/util/fst/FSTSuffixNodeCache.java
+++ b/lucene/core/src/java/org/apache/lucene/util/fst/FSTSuffixNodeCache.java
@@ -17,7 +17,9 @@
 package org.apache.lucene.util.fst;
 
 import java.io.IOException;
+import org.apache.lucene.util.Accountable;
 import org.apache.lucene.util.ByteBlockPool;
+import org.apache.lucene.util.RamUsageEstimator;
 import org.apache.lucene.util.packed.PackedInts;
 import org.apache.lucene.util.packed.PagedGrowableWriter;
 
@@ -48,7 +50,10 @@
  * PagedGrowableWriter} to store the mapping, which allows efficient packing the hash & address long
  * values, and uses {@link ByteBlockPool} to store the actual node content (arcs & outputs).
  */
-final class FSTSuffixNodeCache<T> {
+final class FSTSuffixNodeCache<T> implements Accountable {
+
+  private static final long BASE_RAM_BYTES =
+      RamUsageEstimator.shallowSizeOfInstance(FSTSuffixNodeCache.class);
 
   // primary table -- we add nodes into this until it reaches the requested tableSizeLimit/2, then
   // we move it to fallback
@@ -234,8 +239,18 @@ private long hash(FSTCompiler.UnCompiledNode<T> node) {
     return h;
   }
 
+  @Override
+  public long ramBytesUsed() {
+    long ramBytesUsed = BASE_RAM_BYTES + primaryTable.ramBytesUsed();
+    if (fallbackTable != null) {
+      ramBytesUsed += fallbackTable.ramBytesUsed();
+    }
+    return ramBytesUsed;
+  }
+
   /** Inner class because it needs access to hash function and FST bytes. */
-  class PagedGrowableHash {
+  class PagedGrowableHash implements Accountable {
+
     // storing the FST node address where the position is the masked hash of the node arcs
     private PagedGrowableWriter fstNodeAddress;
     // storing the local copiedNodes address in the same position as fstNodeAddress
@@ -485,5 +500,12 @@ private FST.BytesReader getBytesReader(long nodeAddress, long hashSlot) {
       bytesReader.setPosDelta(nodeAddress - localAddress);
       return bytesReader;
     }
+
+    @Override
+    public long ramBytesUsed() {
+      return copiedNodes.ramBytesUsed()
+          + fstNodeAddress.ramBytesUsed()
+          + copiedNodeAddress.ramBytesUsed();
+    }
   }
 }