diff --git a/modules/core/include/opencv2/core/cvstd.hpp b/modules/core/include/opencv2/core/cvstd.hpp
index ddb53e5325..0a3f553ab8 100644
--- a/modules/core/include/opencv2/core/cvstd.hpp
+++ b/modules/core/include/opencv2/core/cvstd.hpp
@@ -598,6 +598,7 @@ String::String(const char* s)
 {
     if (!s) return;
     size_t len = strlen(s);
+    if (!len) return;
     memcpy(allocate(len), s, len);
 }
 
@@ -665,7 +666,7 @@ String& String::operator=(const char* s)
     deallocate();
     if (!s) return *this;
     size_t len = strlen(s);
-    memcpy(allocate(len), s, len);
+    if (len) memcpy(allocate(len), s, len);
     return *this;
 }
 
@@ -959,8 +960,8 @@ String operator + (const String& lhs, const String& rhs)
 {
     String s;
     s.allocate(lhs.len_ + rhs.len_);
-    memcpy(s.cstr_, lhs.cstr_, lhs.len_);
-    memcpy(s.cstr_ + lhs.len_, rhs.cstr_, rhs.len_);
+    if (lhs.len_) memcpy(s.cstr_, lhs.cstr_, lhs.len_);
+    if (rhs.len_) memcpy(s.cstr_ + lhs.len_, rhs.cstr_, rhs.len_);
     return s;
 }
 
@@ -970,8 +971,8 @@ String operator + (const String& lhs, const char* rhs)
     String s;
     size_t rhslen = strlen(rhs);
     s.allocate(lhs.len_ + rhslen);
-    memcpy(s.cstr_, lhs.cstr_, lhs.len_);
-    memcpy(s.cstr_ + lhs.len_, rhs, rhslen);
+    if (lhs.len_) memcpy(s.cstr_, lhs.cstr_, lhs.len_);
+    if (rhslen) memcpy(s.cstr_ + lhs.len_, rhs, rhslen);
     return s;
 }
 
@@ -981,8 +982,8 @@ String operator + (const char* lhs, const String& rhs)
     String s;
     size_t lhslen = strlen(lhs);
     s.allocate(lhslen + rhs.len_);
-    memcpy(s.cstr_, lhs, lhslen);
-    memcpy(s.cstr_ + lhslen, rhs.cstr_, rhs.len_);
+    if (lhslen) memcpy(s.cstr_, lhs, lhslen);
+    if (rhs.len_) memcpy(s.cstr_ + lhslen, rhs.cstr_, rhs.len_);
     return s;
 }
 
@@ -991,7 +992,7 @@ String operator + (const String& lhs, char rhs)
 {
     String s;
     s.allocate(lhs.len_ + 1);
-    memcpy(s.cstr_, lhs.cstr_, lhs.len_);
+    if (lhs.len_) memcpy(s.cstr_, lhs.cstr_, lhs.len_);
     s.cstr_[lhs.len_] = rhs;
     return s;
 }
@@ -1002,7 +1003,7 @@ String operator + (char lhs, const String& rhs)
     String s;
     s.allocate(rhs.len_ + 1);
     s.cstr_[0] = lhs;
-    memcpy(s.cstr_ + 1, rhs.cstr_, rhs.len_);
+    if (rhs.len_) memcpy(s.cstr_ + 1, rhs.cstr_, rhs.len_);
     return s;
 }
 
diff --git a/modules/core/include/opencv2/core/cvstd.inl.hpp b/modules/core/include/opencv2/core/cvstd.inl.hpp
index 6d4919d995..fb5d8ab1bb 100644
--- a/modules/core/include/opencv2/core/cvstd.inl.hpp
+++ b/modules/core/include/opencv2/core/cvstd.inl.hpp
@@ -80,7 +80,7 @@ String::String(const std::string& str)
     if (!str.empty())
     {
         size_t len = str.size();
-        memcpy(allocate(len), str.c_str(), len);
+        if (len) memcpy(allocate(len), str.c_str(), len);
     }
 }
 
@@ -102,7 +102,7 @@ String& String::operator = (const std::string& str)
     if (!str.empty())
     {
         size_t len = str.size();
-        memcpy(allocate(len), str.c_str(), len);
+        if (len) memcpy(allocate(len), str.c_str(), len);
     }
     return *this;
 }
@@ -126,8 +126,8 @@ String operator + (const String& lhs, const std::string& rhs)
     String s;
     size_t rhslen = rhs.size();
     s.allocate(lhs.len_ + rhslen);
-    memcpy(s.cstr_, lhs.cstr_, lhs.len_);
-    memcpy(s.cstr_ + lhs.len_, rhs.c_str(), rhslen);
+    if (lhs.len_) memcpy(s.cstr_, lhs.cstr_, lhs.len_);
+    if (rhslen) memcpy(s.cstr_ + lhs.len_, rhs.c_str(), rhslen);
     return s;
 }
 
@@ -137,8 +137,8 @@ String operator + (const std::string& lhs, const String& rhs)
     String s;
     size_t lhslen = lhs.size();
     s.allocate(lhslen + rhs.len_);
-    memcpy(s.cstr_, lhs.c_str(), lhslen);
-    memcpy(s.cstr_ + lhslen, rhs.cstr_, rhs.len_);
+    if (lhslen) memcpy(s.cstr_, lhs.c_str(), lhslen);
+    if (rhs.len_) memcpy(s.cstr_ + lhslen, rhs.cstr_, rhs.len_);
     return s;
 }