diff --git a/lib/astutils.cpp b/lib/astutils.cpp
index 2f42dcfba..80dde21d6 100644
--- a/lib/astutils.cpp
+++ b/lib/astutils.cpp
@@ -959,7 +959,7 @@ bool isOppositeCond(bool isNot, bool cpp, const Token * const cond1, const Token
     if (!cond1 || !cond2)
         return false;
 
-    if (cond1->str() == "&&" && cond2->str() == "&&") {
+    if (!isNot && cond1->str() == "&&" && cond2->str() == "&&") {
         for (const Token* tok1: {
         cond1->astOperand1(), cond1->astOperand2()
         }) {
diff --git a/test/testcondition.cpp b/test/testcondition.cpp
index 823947033..5b41aa0e9 100644
--- a/test/testcondition.cpp
+++ b/test/testcondition.cpp
@@ -3658,6 +3658,15 @@ private:
               "  if(b[1] == 2) {}\n"
               "}\n");
         ASSERT_EQUALS("[test.cpp:3]: (style) Condition 'b[1]==2' is always false\n", errout.str());
+
+        // #9878
+        check("void f(bool a, bool b) {\n"
+              "    if (a && b){;}\n"
+              "    else if (!a && b){;}\n"
+              "    else if (!a && !b){;}\n"
+              "    else {;}\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void duplicateCondition() {
diff --git a/test/testother.cpp b/test/testother.cpp
index 99f688320..22b5f7c76 100644
--- a/test/testother.cpp
+++ b/test/testother.cpp
@@ -5310,7 +5310,7 @@ private:
         check("void f(int* x, bool b) {\n"
               "    if ((!x && b) || (x != 0 && b)) {}\n"
               "}\n");
-        ASSERT_EQUALS("[test.cpp:2]: (style) Opposite expression on both sides of '||'.\n", errout.str());
+        ASSERT_EQUALS("", errout.str());
     }
 
     void oppositeExpression() {