diff --git a/tool-testsuite/test/org/antlr/v4/test/tool/TestSymbolIssues.java b/tool-testsuite/test/org/antlr/v4/test/tool/TestSymbolIssues.java
index e51edb65a9..14ae5eff61 100644
--- a/tool-testsuite/test/org/antlr/v4/test/tool/TestSymbolIssues.java
+++ b/tool-testsuite/test/org/antlr/v4/test/tool/TestSymbolIssues.java
@@ -498,4 +498,16 @@ public void testLabelsForTokensWithMixedTypesLRWithoutLabels() {
 
 		testErrors(test, false);
 	}
+
+	@Test public void testNotImpliedCharactersWithCaseInsensitiveOption() {
+		String[] test = {
+				"lexer grammar Test;\n" +
+				"options { caseInsensitive=true; }\n" +
+				"TOKEN: [A-z];",
+
+				"warning(" + ErrorType.RANGE_PROBABLY_CONTAINS_NOT_IMPLIED_CHARACTERS.code + "): Test.g4:3:7: Range A..z probably contains not implied characters [\\]^_`. Both bounds should be defined in lower or UPPER case\n"
+		};
+
+		testErrors(test, false);
+	}
 }
diff --git a/tool/src/org/antlr/v4/automata/CharactersDataCheckStatus.java b/tool/src/org/antlr/v4/automata/CharactersDataCheckStatus.java
new file mode 100644
index 0000000000..be0ffcf5d9
--- /dev/null
+++ b/tool/src/org/antlr/v4/automata/CharactersDataCheckStatus.java
@@ -0,0 +1,11 @@
+package org.antlr.v4.automata;
+
+public class CharactersDataCheckStatus {
+	public final boolean collision;
+	public final boolean notImpliedCharacters;
+
+	public CharactersDataCheckStatus(boolean collision, boolean notImpliedCharacters) {
+		this.collision = collision;
+		this.notImpliedCharacters = notImpliedCharacters;
+	}
+}
diff --git a/tool/src/org/antlr/v4/automata/LexerATNFactory.java b/tool/src/org/antlr/v4/automata/LexerATNFactory.java
index 65d65afd26..5f39325d67 100644
--- a/tool/src/org/antlr/v4/automata/LexerATNFactory.java
+++ b/tool/src/org/antlr/v4/automata/LexerATNFactory.java
@@ -279,7 +279,7 @@ public Handle set(GrammarAST associatedAST, List<GrammarAST> alts, boolean inver
 				int a = CharSupport.getCharValueFromGrammarCharLiteral(t.getChild(0).getText());
 				int b = CharSupport.getCharValueFromGrammarCharLiteral(t.getChild(1).getText());
 				if (checkRange((GrammarAST)t.getChild(0), (GrammarAST)t.getChild(1), a, b)) {
-					checkRangeAndAddToSet(associatedAST, t, set, a, b, caseInsensitive, true);
+					checkRangeAndAddToSet(associatedAST, t, set, a, b, caseInsensitive, null);
 				}
 			}
 			else if ( t.getType()==ANTLRParser.LEXER_CHAR_SET ) {
@@ -567,28 +567,31 @@ private void applyPrevState(GrammarAST charSetAST, IntervalSet set, CharSetParse
 	}
 
 	private void checkCharAndAddToSet(GrammarAST ast, IntervalSet set, int c) {
-		checkRangeAndAddToSet(ast, ast, set, c, c, caseInsensitive, true);
+		checkRangeAndAddToSet(ast, ast, set, c, c, caseInsensitive, null);
 	}
 
 	private void checkRangeAndAddToSet(GrammarAST mainAst, IntervalSet set, int a, int b) {
-		checkRangeAndAddToSet(mainAst, mainAst, set, a, b, caseInsensitive, true);
+		checkRangeAndAddToSet(mainAst, mainAst, set, a, b, caseInsensitive, null);
 	}
 
-	private boolean checkRangeAndAddToSet(GrammarAST rootAst, GrammarAST ast, IntervalSet set, int a, int b, boolean caseInsensitive, boolean reportCollision) {
-		boolean charactersCollision = false;
-		RangeBorderCharactersData charactersData = RangeBorderCharactersData.getAndCheckCharactersData(a, b, g, ast);
+	private CharactersDataCheckStatus checkRangeAndAddToSet(GrammarAST rootAst, GrammarAST ast, IntervalSet set, int a, int b, boolean caseInsensitive, CharactersDataCheckStatus previousStatus) {
+		CharactersDataCheckStatus status;
+		RangeBorderCharactersData charactersData = RangeBorderCharactersData.getAndCheckCharactersData(a, b, g, ast,
+				previousStatus == null || !previousStatus.notImpliedCharacters);
 		if (caseInsensitive) {
+			status = new CharactersDataCheckStatus(false, charactersData.mixOfLowerAndUpperCharCase);
 			if (charactersData.isSingleRange()) {
-				checkRangeAndAddToSet(rootAst, ast, set, a, b, false, true);
+				status = checkRangeAndAddToSet(rootAst, ast, set, a, b, false, status);
 			}
 			else {
-				charactersCollision = checkRangeAndAddToSet(rootAst, ast, set, charactersData.lowerFrom, charactersData.lowerTo, false, true);
+				status = checkRangeAndAddToSet(rootAst, ast, set, charactersData.lowerFrom, charactersData.lowerTo, false, status);
 				// Don't report similar warning twice
-				checkRangeAndAddToSet(rootAst, ast, set, charactersData.upperFrom, charactersData.upperTo, false, !charactersCollision);
+				status = checkRangeAndAddToSet(rootAst, ast, set, charactersData.upperFrom, charactersData.upperTo, false, status);
 			}
 		}
 		else {
-			if (reportCollision) {
+			boolean charactersCollision = previousStatus != null && previousStatus.collision;
+			if (!charactersCollision) {
 				for (int i = a; i <= b; i++) {
 					if (set.contains(i)) {
 						String setText;
@@ -611,20 +614,22 @@ private boolean checkRangeAndAddToSet(GrammarAST rootAst, GrammarAST ast, Interv
 							sb.replace(sb.length() - 3, sb.length(), "");
 							setText = sb.toString();
 						}
+						String charsString = a == b ? String.valueOf((char)a) : (char) a + "-" + (char) b;
 						g.tool.errMgr.grammarError(ErrorType.CHARACTERS_COLLISION_IN_SET, g.fileName, ast.getToken(),
-								(char) a + "-" + (char) b, setText);
+								charsString, setText);
 						charactersCollision = true;
 						break;
 					}
 				}
 			}
+			status = new CharactersDataCheckStatus(charactersCollision, charactersData.mixOfLowerAndUpperCharCase);
 			set.add(a, b);
 		}
-		return charactersCollision;
+		return status;
 	}
 
 	private Transition createTransition(ATNState target, int from, int to, CommonTree tree) {
-		RangeBorderCharactersData charactersData = RangeBorderCharactersData.getAndCheckCharactersData(from, to, g, tree);
+		RangeBorderCharactersData charactersData = RangeBorderCharactersData.getAndCheckCharactersData(from, to, g, tree, true);
 		if (caseInsensitive) {
 			if (charactersData.isSingleRange()) {
 				return CodePointTransitions.createWithCodePointRange(target, from, to);
diff --git a/tool/src/org/antlr/v4/automata/RangeBorderCharactersData.java b/tool/src/org/antlr/v4/automata/RangeBorderCharactersData.java
index 7c30c0feb6..4bc44adf60 100644
--- a/tool/src/org/antlr/v4/automata/RangeBorderCharactersData.java
+++ b/tool/src/org/antlr/v4/automata/RangeBorderCharactersData.java
@@ -19,7 +19,9 @@ public RangeBorderCharactersData(int lowerFrom, int upperFrom, int lowerTo, int
 		this.mixOfLowerAndUpperCharCase = mixOfLowerAndUpperCharCase;
 	}
 
-	public static RangeBorderCharactersData getAndCheckCharactersData(int from, int to, Grammar grammar, CommonTree tree) {
+	public static RangeBorderCharactersData getAndCheckCharactersData(int from, int to, Grammar grammar, CommonTree tree,
+																	  boolean reportRangeContainsNotImpliedCharacters
+	) {
 		int lowerFrom = Character.toLowerCase(from);
 		int upperFrom = Character.toUpperCase(from);
 		int lowerTo = Character.toLowerCase(to);
@@ -28,7 +30,7 @@ public static RangeBorderCharactersData getAndCheckCharactersData(int from, int
 		boolean isLowerFrom = lowerFrom == from;
 		boolean isLowerTo = lowerTo == to;
 		boolean mixOfLowerAndUpperCharCase = isLowerFrom && !isLowerTo || !isLowerFrom && isLowerTo;
-		if (mixOfLowerAndUpperCharCase && from <= 0x7F && to <= 0x7F) {
+		if (reportRangeContainsNotImpliedCharacters && mixOfLowerAndUpperCharCase && from <= 0x7F && to <= 0x7F) {
 			StringBuilder notImpliedCharacters = new StringBuilder();
 			for (int i = from; i < to; i++) {
 				if (!Character.isAlphabetic(i)) {