diff --git a/lib/checkother.cpp b/lib/checkother.cpp
index 7a06f66f644..dbc16f2d8ac 100644
--- a/lib/checkother.cpp
+++ b/lib/checkother.cpp
@@ -2023,7 +2023,7 @@ void CheckOther::checkCharVariable()
                 if (!tok->variable()->isArray() && !tok->variable()->isPointer())
                     continue;
                 const Token *index = tok->next()->astOperand2();
-                if (warning && tok->variable()->isArray() && astIsSignedChar(index) && index->getValueGE(0x80, *mSettings))
+                if (warning && astIsSignedChar(index) && index->getValueLE(-1, *mSettings))
                     signedCharArrayIndexError(tok);
                 if (portability && astIsUnknownSignChar(index) && index->getValueGE(0x80, *mSettings))
                     unknownSignCharArrayIndexError(tok);
diff --git a/lib/token.cpp b/lib/token.cpp
index 98f79b4bb1d..400f07228fb 100644
--- a/lib/token.cpp
+++ b/lib/token.cpp
@@ -1922,6 +1922,7 @@ const ValueFlow::Value * Token::getValueLE(const MathLib::bigint val, const Sett
 {
     if (!mImpl->mValues)
         return nullptr;
+    // TODO: assert the given value is actually possible - i.e. 0x80 for a signed char is not possible
     return ValueFlow::findValue(*mImpl->mValues, settings, [&](const ValueFlow::Value& v) {
         return !v.isImpossible() && v.isIntValue() && v.intvalue <= val;
     });
@@ -1931,6 +1932,7 @@ const ValueFlow::Value * Token::getValueGE(const MathLib::bigint val, const Sett
 {
     if (!mImpl->mValues)
         return nullptr;
+    // TODO: assert the given value is actually possible - i.e. 0x80 for a signed char is not possible
     return ValueFlow::findValue(*mImpl->mValues, settings, [&](const ValueFlow::Value& v) {
         return !v.isImpossible() && v.isIntValue() && v.intvalue >= val;
     });
@@ -1940,6 +1942,7 @@ const ValueFlow::Value * Token::getValueNE(MathLib::bigint val) const
 {
     if (!mImpl->mValues)
         return nullptr;
+    // TODO: assert the given value is actually possible - i.e. 0x80 for a signed char is not possible
     const auto it = std::find_if(mImpl->mValues->cbegin(), mImpl->mValues->cend(), [=](const ValueFlow::Value& value) {
         return value.isIntValue() && !value.isImpossible() && value.intvalue != val;
     });
diff --git a/test/testcharvar.cpp b/test/testcharvar.cpp
index 624efcff539..f2fd4b3653a 100644
--- a/test/testcharvar.cpp
+++ b/test/testcharvar.cpp
@@ -60,6 +60,14 @@ class TestCharVar : public TestFixture {
               "}");
         ASSERT_EQUALS("", errout_str());
 
+        check("int buf[256];\n"
+              "void foo()\n"
+              "{\n"
+              "    signed char ch = 0x80;\n"
+              "    buf[ch] = 0;\n"
+              "}");
+        ASSERT_EQUALS("[test.cpp:5:5]: (warning) Signed 'char' type used as array index. [signedCharArrayIndex]\n", errout_str());
+
         check("int buf[256];\n"
               "void foo()\n"
               "{\n"
@@ -71,7 +79,7 @@ class TestCharVar : public TestFixture {
         check("int buf[256];\n"
               "void foo()\n"
               "{\n"
-              "    char ch = 0;\n"
+              "    unsigned char ch = 0;\n"
               "    buf[ch] = 0;\n"
               "}");
         ASSERT_EQUALS("", errout_str());
@@ -87,10 +95,17 @@ class TestCharVar : public TestFixture {
         check("int buf[256];\n"
               "void foo()\n"
               "{\n"
-              "    char ch = 0x80;\n"
+              "    char ch = 0;\n"
               "    buf[ch] = 0;\n"
               "}");
-        ASSERT_EQUALS("[test.cpp:5:5]: (portability) 'char' type used as array index. [unknownSignCharArrayIndex]\n", errout_str());
+        ASSERT_EQUALS("", errout_str());
+
+        check("int buf[256];\n"
+              "void foo(unsigned char ch)\n"
+              "{\n"
+              "    buf[ch] = 0;\n"
+              "}");
+        ASSERT_EQUALS("", errout_str());
 
         check("int buf[256];\n"
               "void foo(signed char ch)\n"
@@ -106,6 +121,20 @@ class TestCharVar : public TestFixture {
               "}");
         ASSERT_EQUALS("", errout_str());
 
+        check("void foo(char* buf)\n"
+              "{\n"
+              "    unsigned char ch = 0x80;"
+              "    buf[ch] = 0;\n"
+              "}");
+        ASSERT_EQUALS("", errout_str());
+
+        check("void foo(char* buf)\n"
+              "{\n"
+              "    signed char ch = 0x80;"
+              "    buf[ch] = 0;\n"
+              "}");
+        ASSERT_EQUALS("[test.cpp:3:31]: (warning) Signed 'char' type used as array index. [signedCharArrayIndex]\n", errout_str());
+
         check("void foo(char* buf)\n"
               "{\n"
               "    char ch = 0x80;"
@@ -113,6 +142,20 @@ class TestCharVar : public TestFixture {
               "}");
         ASSERT_EQUALS("[test.cpp:3:24]: (portability) 'char' type used as array index. [unknownSignCharArrayIndex]\n", errout_str());
 
+        check("void foo(char* buf)\n"
+              "{\n"
+              "    unsigned char ch = 0;"
+              "    buf[ch] = 0;\n"
+              "}");
+        ASSERT_EQUALS("", errout_str());
+
+        check("void foo(char* buf)\n"
+              "{\n"
+              "    signed char ch = 0;"
+              "    buf[ch] = 0;\n"
+              "}");
+        ASSERT_EQUALS("", errout_str());
+
         check("void foo(char* buf)\n"
               "{\n"
               "    char ch = 0;"
@@ -126,6 +169,18 @@ class TestCharVar : public TestFixture {
               "}");
         ASSERT_EQUALS("", errout_str());
 
+        check("void foo(char* buf, unsigned char ch)\n"
+              "{\n"
+              "    buf[ch] = 0;\n"
+              "}");
+        ASSERT_EQUALS("", errout_str());
+
+        check("void foo(char* buf, signed char ch)\n"
+              "{\n"
+              "    buf[ch] = 0;\n"
+              "}");
+        ASSERT_EQUALS("", errout_str());
+
         check("void foo(char* buf, char ch)\n"
               "{\n"
               "    buf[ch] = 0;\n"
@@ -135,7 +190,7 @@ class TestCharVar : public TestFixture {
         check("int flags[256];\n"
               "void foo(const char* str)\n"
               "{\n"
-              "    flags[*str] = 0;\n"
+              "    flags[(signed char)*str] = 0;\n"
               "}");
         ASSERT_EQUALS("", errout_str());
 
@@ -146,6 +201,13 @@ class TestCharVar : public TestFixture {
               "}");
         ASSERT_EQUALS("", errout_str());
 
+        check("int flags[256];\n"
+              "void foo(const char* str)\n"
+              "{\n"
+              "    flags[*str] = 0;\n"
+              "}");
+        ASSERT_EQUALS("", errout_str());
+
         check("void foo(const char str[])\n"
               "{\n"
               "    map[str] = 0;\n"