diff --git a/drools-core/src/main/java/org/drools/core/util/index/IndexUtil.java b/drools-core/src/main/java/org/drools/core/util/index/IndexUtil.java
index b48d47a9c07..67e74d06b7d 100644
--- a/drools-core/src/main/java/org/drools/core/util/index/IndexUtil.java
+++ b/drools-core/src/main/java/org/drools/core/util/index/IndexUtil.java
@@ -66,7 +66,7 @@ public static boolean compositeAllowed(BetaNodeFieldConstraint[] constraints, sh
     }
 
     public static boolean isIndexable(BetaNodeFieldConstraint constraint, short nodeType, RuleBaseConfiguration config) {
-        return constraint instanceof IndexableConstraint && ((IndexableConstraint)constraint).isIndexable(nodeType, config);
+        return constraint instanceof IndexableConstraint && ((IndexableConstraint)constraint).isIndexable(nodeType, config) && !isBigDecimalEqualityConstraint((IndexableConstraint)constraint);
     }
 
     private static boolean canHaveRangeIndex(short nodeType, IndexableConstraint constraint, RuleBaseConfiguration config) {
diff --git a/drools-core/src/test/java/org/drools/core/util/index/IndexUtilTest.java b/drools-core/src/test/java/org/drools/core/util/index/IndexUtilTest.java
index f700b1dcdc8..1edb34d1569 100644
--- a/drools-core/src/test/java/org/drools/core/util/index/IndexUtilTest.java
+++ b/drools-core/src/test/java/org/drools/core/util/index/IndexUtilTest.java
@@ -125,7 +125,7 @@ public void isIndexableForNodeWithIntAndBigDecimalAndString() {
     }
 
     @Test
-    public void isIndexableForNodeWithBigDecimal() {
+    public void isIndexableForJoinNodeWithBigDecimal() {
         RuleBaseConfiguration config = new RuleBaseConfiguration();
         FakeBetaNodeFieldConstraint bigDecimalEqualsConstraint = new FakeBetaNodeFieldConstraint(IndexUtil.ConstraintType.EQUAL, new FakeInternalReadAccessor(ValueType.BIG_DECIMAL_TYPE));
         BetaNodeFieldConstraint[] constraints = new FakeBetaNodeFieldConstraint[]{bigDecimalEqualsConstraint};
@@ -133,6 +133,24 @@ public void isIndexableForNodeWithBigDecimal() {
         assertThat(indexed).as("BigDecimal is not indexed").containsExactly(false);
     }
 
+    @Test
+    public void isIndexableForExistsNodeWithBigDecimal() {
+        RuleBaseConfiguration config = new RuleBaseConfiguration();
+        FakeBetaNodeFieldConstraint bigDecimalEqualsConstraint = new FakeBetaNodeFieldConstraint(IndexUtil.ConstraintType.EQUAL, new FakeInternalReadAccessor(ValueType.BIG_DECIMAL_TYPE));
+        BetaNodeFieldConstraint[] constraints = new FakeBetaNodeFieldConstraint[]{bigDecimalEqualsConstraint};
+        boolean[] indexed = IndexUtil.isIndexableForNode(IndexPrecedenceOption.EQUALITY_PRIORITY, NodeTypeEnums.ExistsNode, config.getCompositeKeyDepth(), constraints, config);
+        assertThat(indexed).as("BigDecimal is not indexed").containsExactly(false);
+    }
+
+    @Test
+    public void isIndexableForNotNodeWithBigDecimal() {
+        RuleBaseConfiguration config = new RuleBaseConfiguration();
+        FakeBetaNodeFieldConstraint bigDecimalEqualsConstraint = new FakeBetaNodeFieldConstraint(IndexUtil.ConstraintType.EQUAL, new FakeInternalReadAccessor(ValueType.BIG_DECIMAL_TYPE));
+        BetaNodeFieldConstraint[] constraints = new FakeBetaNodeFieldConstraint[]{bigDecimalEqualsConstraint};
+        boolean[] indexed = IndexUtil.isIndexableForNode(IndexPrecedenceOption.EQUALITY_PRIORITY, NodeTypeEnums.NotNode, config.getCompositeKeyDepth(), constraints, config);
+        assertThat(indexed).as("BigDecimal is not indexed").containsExactly(false);
+    }
+
     static class FakeBetaNodeFieldConstraint implements BetaNodeFieldConstraint,
                                              IndexableConstraint {
 
@@ -202,7 +220,7 @@ public boolean isUnification() {
 
         @Override
         public boolean isIndexable(short nodeType, RuleBaseConfiguration config) {
-            return false;
+            return constraintType.isIndexableForNode(nodeType, this, config);
         }
 
         @Override
diff --git a/drools-test-coverage/test-compiler-integration/src/test/java/org/drools/compiler/integrationtests/operators/ExistsTest.java b/drools-test-coverage/test-compiler-integration/src/test/java/org/drools/compiler/integrationtests/operators/ExistsTest.java
index 293674df95f..c57beef8392 100644
--- a/drools-test-coverage/test-compiler-integration/src/test/java/org/drools/compiler/integrationtests/operators/ExistsTest.java
+++ b/drools-test-coverage/test-compiler-integration/src/test/java/org/drools/compiler/integrationtests/operators/ExistsTest.java
@@ -16,6 +16,7 @@
 
 package org.drools.compiler.integrationtests.operators;
 
+import java.math.BigDecimal;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
@@ -285,4 +286,187 @@ public void testSharedExistsWithNot() {
             ksession.dispose();
         }
     }
+
+    @Test
+    public void existsAndNotWithSingleCoercion_shouldNotMatchExists() {
+        // KIE-766
+        final String drl =
+                "package org.drools.compiler.integrationtests.operators;\n" +
+                           "import " + StringHolder.class.getCanonicalName() + "\n" +
+                           "import " + BDHolder.class.getCanonicalName() + "\n" +
+                           "global java.util.List list \n" +
+                           "rule R1\n" +
+                           "  when\n" +
+                           "    $stringHolder : StringHolder( $value1 : value1 )\n" +
+                           "    exists BDHolder( $value1 == value1 )\n" +
+                           "  then\n" +
+                           "    list.add(\"R1\");\n" +
+                           "end\n" +
+                           "rule R2\n" +
+                           "  when\n" +
+                           "    $stringHolder : StringHolder( $value1 : value1 )\n" +
+                           "    not BDHolder( $value1 == value1 )\n" +
+                           "  then\n" +
+                           "    list.add(\"R2\");\n" +
+                           "end\n";
+
+        final KieBase kbase = KieBaseUtil.getKieBaseFromKieModuleFromDrl("exists-test",
+                                                                         kieBaseTestConfiguration,
+                                                                         drl);
+        final KieSession ksession = kbase.newKieSession();
+        try {
+            final List<String> list = new ArrayList<>();
+            ksession.setGlobal("list", list);
+
+            ksession.insert(new StringHolder("9999", "567"));
+            ksession.insert(new BDHolder(new BigDecimal("0"), new BigDecimal("567")));
+            ksession.fireAllRules();
+
+            assertThat(list).hasSize(1);
+            assertThat(list).as("BDHolder shouldn't match the exists constraints").containsExactly("R2");
+        } finally {
+            ksession.dispose();
+        }
+    }
+
+    @Test
+    public void existsAndNotWithMultipleCoercion_shouldNotMatchExists() {
+        // KIE-766
+        final String drl =
+                "package org.drools.compiler.integrationtests.operators;\n" +
+                           "import " + StringHolder.class.getCanonicalName() + "\n" +
+                           "import " + BDHolder.class.getCanonicalName() + "\n" +
+                           "global java.util.List list \n" +
+                           "rule R1\n" +
+                           "  when\n" +
+                           "    $stringHolder : StringHolder( $value1 : value1, $value2 : value2 )\n" +
+                           "    exists BDHolder( $value1 == value1, $value2 == value2 )\n" +
+                           "  then\n" +
+                           "    list.add(\"R1\");\n" +
+                           "end\n" +
+                           "rule R2\n" +
+                           "  when\n" +
+                           "    $stringHolder : StringHolder( $value1 : value1, $value2 : value2 )\n" +
+                           "    not BDHolder( $value1 == value1, $value2 == value2 )\n" +
+                           "  then\n" +
+                           "    list.add(\"R2\");\n" +
+                           "end\n";
+
+        final KieBase kbase = KieBaseUtil.getKieBaseFromKieModuleFromDrl("exists-test",
+                                                                         kieBaseTestConfiguration,
+                                                                         drl);
+        final KieSession ksession = kbase.newKieSession();
+        try {
+            final List<String> list = new ArrayList<>();
+            ksession.setGlobal("list", list);
+
+            ksession.insert(new StringHolder("9999", "567"));
+            ksession.insert(new BDHolder(new BigDecimal("0"), new BigDecimal("567")));
+            ksession.fireAllRules();
+
+            assertThat(list).hasSize(1);
+            assertThat(list).as("BDHolder shouldn't match the exists constraints").containsExactly("R2");
+        } finally {
+            ksession.dispose();
+        }
+    }
+
+    @Test
+    public void existsAndNotWithBigDecimals_shouldNotMatchExists() {
+        // KIE-766
+        final String drl =
+                "package org.drools.compiler.integrationtests.operators;\n" +
+                           "import " + BDHolder.class.getCanonicalName() + "\n" +
+                           "global java.util.List list \n" +
+                           "rule R1\n" +
+                           "  when\n" +
+                           "    $bdHolder1 : BDHolder( $value1 : value1, $value2 : value2 )\n" +
+                           "    exists BDHolder( this != $bdHolder1, $value1 == value1, $value2 == value2 )\n" +
+                           "  then\n" +
+                           "    list.add(\"R1\");\n" +
+                           "end\n" +
+                           "rule R2\n" +
+                           "  when\n" +
+                           "    $bdHolder1 : BDHolder( $value1 : value1, $value2 : value2 )\n" +
+                           "    not BDHolder( this != $bdHolder1, $value1 == value1, $value2 == value2 )\n" +
+                           "  then\n" +
+                           "    list.add(\"R2\");\n" +
+                           "end\n";
+
+        final KieBase kbase = KieBaseUtil.getKieBaseFromKieModuleFromDrl("exists-test",
+                                                                         kieBaseTestConfiguration,
+                                                                         drl);
+        final KieSession ksession = kbase.newKieSession();
+        try {
+            final List<String> list = new ArrayList<>();
+            ksession.setGlobal("list", list);
+
+            ksession.insert(new BDHolder(new BigDecimal("9999"), new BigDecimal("567")));
+            ksession.insert(new BDHolder(new BigDecimal("0"), new BigDecimal("567")));
+            ksession.fireAllRules();
+
+            assertThat(list).hasSize(2);
+            assertThat(list).as("BDHolder shouldn't match the exists constraints. R2 fires twice because 2 objects can match as $bdHolder1")
+                            .containsExactly("R2", "R2");
+        } finally {
+            ksession.dispose();
+        }
+    }
+
+    public static class StringHolder {
+
+        private String value1;
+        private String value2;
+
+        public StringHolder(String value1, String value2) {
+            this.value1 = value1;
+            this.value2 = value2;
+        }
+
+        public String getValue1() {
+            return value1;
+        }
+
+        public void setValue1(String value1) {
+            this.value1 = value1;
+        }
+
+        public String getValue2() {
+            return value2;
+        }
+
+        public void setValue2(String value2) {
+            this.value2 = value2;
+        }
+
+    }
+
+    public static class BDHolder {
+
+        private BigDecimal value1;
+        private BigDecimal value2;
+
+        public BDHolder(BigDecimal value1, BigDecimal value2) {
+            super();
+            this.value1 = value1;
+            this.value2 = value2;
+        }
+
+        public BigDecimal getValue1() {
+            return value1;
+        }
+
+        public void setValue1(BigDecimal value1) {
+            this.value1 = value1;
+        }
+
+        public BigDecimal getValue2() {
+            return value2;
+        }
+
+        public void setValue2(BigDecimal value2) {
+            this.value2 = value2;
+        }
+
+    }
 }