diff --git a/modules/core/test/test_misc.cpp b/modules/core/test/test_misc.cpp
index 3934ceb716..372aab7eb0 100644
--- a/modules/core/test/test_misc.cpp
+++ b/modules/core/test/test_misc.cpp
@@ -189,7 +189,7 @@ TEST(Core_OutputArrayCreate, _13772)
 TEST(Core_String, find_last_of__with__empty_string)
 {
     cv::String s;
-    size_t p = s.find_last_of("q", 0);
+    size_t p = s.find_last_of('q', 0);
     // npos is not exported: EXPECT_EQ(cv::String::npos, p);
     EXPECT_EQ(std::string::npos, p);
 }
diff --git a/modules/dnn/src/darknet/darknet_io.cpp b/modules/dnn/src/darknet/darknet_io.cpp
index c745d5f036..f6d71fd6d4 100644
--- a/modules/dnn/src/darknet/darknet_io.cpp
+++ b/modules/dnn/src/darknet/darknet_io.cpp
@@ -620,7 +620,7 @@ namespace cv {
                             // read section
                             read_net = false;
                             ++layers_counter;
-                            const size_t layer_type_size = line.find("]") - 1;
+                            const size_t layer_type_size = line.find(']') - 1;
                             CV_Assert(layer_type_size < line.size());
                             std::string layer_type = line.substr(1, layer_type_size);
                             net->layers_cfg[layers_counter]["layer_type"] = layer_type;
diff --git a/modules/dnn/src/tensorflow/tf_importer.cpp b/modules/dnn/src/tensorflow/tf_importer.cpp
index 13e1f40cd6..493f0ec305 100644
--- a/modules/dnn/src/tensorflow/tf_importer.cpp
+++ b/modules/dnn/src/tensorflow/tf_importer.cpp
@@ -389,7 +389,7 @@ Pin parsePin(const std::string &name)
 {
     Pin pin(name);
 
-    size_t delimiter_pos = name.find_first_of(":");
+    size_t delimiter_pos = name.find_first_of(':');
     if (delimiter_pos != std::string::npos)
     {
         pin.name = name.substr(0, delimiter_pos);