diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/LexerATNSimulator.java b/runtime/Java/src/org/antlr/v4/runtime/atn/LexerATNSimulator.java
index 3665d1e92..e635dd95f 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/LexerATNSimulator.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/LexerATNSimulator.java
@@ -602,7 +602,7 @@ public class LexerATNSimulator extends ATNSimulator {
 		}
 
 		DFA dfa = decisionToDFA[mode];
-		synchronized (dfa) {
+		synchronized (p) {
 			if ( p.edges==null ) {
 				//  make room for tokens 1..n and -1 masquerading as index 0
 				p.edges = new DFAState[MAX_DFA_EDGE-MIN_DFA_EDGE+1];
@@ -641,7 +641,7 @@ public class LexerATNSimulator extends ATNSimulator {
 		}
 
 		DFA dfa = decisionToDFA[mode];
-		synchronized (dfa) {
+		synchronized (dfa.states) {
 			DFAState existing = dfa.states.get(proposed);
 			if ( existing!=null ) return existing;
 
@@ -650,7 +650,7 @@ public class LexerATNSimulator extends ATNSimulator {
 			newState.stateNumber = dfa.states.size();
 			configs.setReadonly(true);
 			newState.configs = configs;
-			decisionToDFA[mode].states.put(newState, newState);
+			dfa.states.put(newState, newState);
 			return newState;
 		}
 	}
diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/ParserATNSimulator.java b/runtime/Java/src/org/antlr/v4/runtime/atn/ParserATNSimulator.java
index fc7e94e10..b1ad17a26 100755
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/ParserATNSimulator.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/ParserATNSimulator.java
@@ -1546,7 +1546,7 @@ public class ParserATNSimulator extends ATNSimulator {
 		if ( debug ) System.out.println("EDGE "+from+" -> "+to+" upon "+getTokenName(t));
 		if ( from==null || t < -1 || to == null ) return;
 		to = addDFAState(dfa, to); // used existing if possible not incoming
-		synchronized (dfa) {
+		synchronized (from) {
 			if ( from.edges==null ) {
 				from.edges = new DFAState[atn.maxTokenType+1+1]; // TODO: make adaptive
 			}
@@ -1557,7 +1557,7 @@ public class ParserATNSimulator extends ATNSimulator {
 
 	/** Add D if not there and return D. Return previous if already present. */
 	protected DFAState addDFAState(@NotNull DFA dfa, @NotNull DFAState D) {
-		synchronized (dfa) {
+		synchronized (dfa.states) {
 			DFAState existing = dfa.states.get(D);
 			if ( existing!=null ) return existing;