diff --git a/cores/esp8266/WString.cpp b/cores/esp8266/WString.cpp
index 056bbeb98..3dda69bda 100644
--- a/cores/esp8266/WString.cpp
+++ b/cores/esp8266/WString.cpp
@@ -617,17 +617,33 @@ int String::indexOf(char ch, unsigned int fromIndex) const {
     return temp - buffer();
 }
 
+int String::indexOf(const __FlashStringHelper *s2) const {
+    return indexOf(s2, 0);
+}
+
+int String::indexOf(const __FlashStringHelper *s2, unsigned int fromIndex) const {
+    return indexOf((const char*) s2, fromIndex);
+}
+
+int String::indexOf(const char *s2) const {
+    return indexOf(s2, 0);
+}
+
+int String::indexOf(const char *s2, unsigned int fromIndex) const {
+    if (fromIndex >= len())
+        return -1;
+    const char *found = strstr_P(buffer() + fromIndex, s2);
+    if (found == NULL)
+        return -1;
+    return found - buffer();
+}
+
 int String::indexOf(const String &s2) const {
     return indexOf(s2, 0);
 }
 
 int String::indexOf(const String &s2, unsigned int fromIndex) const {
-    if (fromIndex >= len())
-        return -1;
-    const char *found = strstr(buffer() + fromIndex, s2.buffer());
-    if (found == NULL)
-        return -1;
-    return found - buffer();
+    return indexOf(s2.c_str(), fromIndex);
 }
 
 int String::lastIndexOf(char theChar) const {
diff --git a/cores/esp8266/WString.h b/cores/esp8266/WString.h
index c9b79f21c..262cfda0a 100644
--- a/cores/esp8266/WString.h
+++ b/cores/esp8266/WString.h
@@ -235,6 +235,10 @@ class String {
         // search
         int indexOf(char ch) const;
         int indexOf(char ch, unsigned int fromIndex) const;
+        int indexOf(const char *str) const;
+        int indexOf(const char *str, unsigned int fromIndex) const;
+        int indexOf(const __FlashStringHelper *str) const;
+        int indexOf(const __FlashStringHelper *str, unsigned int fromIndex) const;
         int indexOf(const String &str) const;
         int indexOf(const String &str, unsigned int fromIndex) const;
         int lastIndexOf(char ch) const;
diff --git a/tests/host/core/test_string.cpp b/tests/host/core/test_string.cpp
index f9fb30a6d..1150ba591 100644
--- a/tests/host/core/test_string.cpp
+++ b/tests/host/core/test_string.cpp
@@ -245,6 +245,10 @@ TEST_CASE("String nulls", "[core][String]")
     REQUIRE(s.lastIndexOf("tacos") == -1);
     REQUIRE(s.lastIndexOf('t', 0) == -1);
     REQUIRE(s.lastIndexOf('t') == -1);
+    REQUIRE(s.indexOf(String("tacos"), 1) == -1);
+    REQUIRE(s.indexOf(String("tacos")) == -1);
+    REQUIRE(s.indexOf(F("tacos"), 1) == -1);
+    REQUIRE(s.indexOf(F("tacos")) == -1);
     REQUIRE(s.indexOf("tacos", 1) == -1);
     REQUIRE(s.indexOf("tacos") == -1);
     REQUIRE(s.indexOf('t', 1) == -1);