diff --git a/Sha/sha1.cpp b/Sha/sha1.cpp
index 9ff3a1c..c2f30e2 100644
--- a/Sha/sha1.cpp
+++ b/Sha/sha1.cpp
@@ -72,9 +72,17 @@ void Sha1Class::addUncounted(uint8_t data) {
   }
 }
 
-void Sha1Class::write(uint8_t data) {
+#if defined(ARDUINO) && ARDUINO >= 100
+size_t
+#else
+void
+#endif
+Sha1Class::write(uint8_t data) {
   ++byteCount;
   addUncounted(data);
+#if defined(ARDUINO) && ARDUINO >= 100
+  return 1;
+#endif
 }
 
 void Sha1Class::pad() {
diff --git a/Sha/sha1.h b/Sha/sha1.h
index 9975660..e067362 100644
--- a/Sha/sha1.h
+++ b/Sha/sha1.h
@@ -23,7 +23,11 @@ class Sha1Class : public Print
     void initHmac(const uint8_t* secret, int secretLength);
     uint8_t* result(void);
     uint8_t* resultHmac(void);
+#if defined(ARDUINO) && ARDUINO >= 100
+    virtual size_t write(uint8_t);
+#else
     virtual void write(uint8_t);
+#endif
     using Print::write;
   private:
     void pad();
diff --git a/Sha/sha256.cpp b/Sha/sha256.cpp
index e479d86..a35d5d3 100644
--- a/Sha/sha256.cpp
+++ b/Sha/sha256.cpp
@@ -87,9 +87,17 @@ void Sha256Class::addUncounted(uint8_t data) {
   }
 }
 
-void Sha256Class::write(uint8_t data) {
+#if defined(ARDUINO) && ARDUINO >= 100
+size_t
+#else
+void
+#endif
+Sha256Class::write(uint8_t data) {
   ++byteCount;
   addUncounted(data);
+#if defined(ARDUINO) && ARDUINO >= 100
+  return 1;
+#endif
 }
 
 void Sha256Class::pad() {
diff --git a/Sha/sha256.h b/Sha/sha256.h
index b4b5fd4..b9f4d08 100644
--- a/Sha/sha256.h
+++ b/Sha/sha256.h
@@ -23,7 +23,11 @@ class Sha256Class : public Print
     void initHmac(const uint8_t* secret, int secretLength);
     uint8_t* result(void);
     uint8_t* resultHmac(void);
+#if defined(ARDUINO) && ARDUINO >= 100
+    virtual size_t write(uint8_t);
+#else
     virtual void write(uint8_t);
+#endif
     using Print::write;
   private:
     void pad();