diff --git a/include/mapnik/boolean.hpp b/include/mapnik/boolean.hpp
index 122604fc0..171cbd7b8 100644
--- a/include/mapnik/boolean.hpp
+++ b/include/mapnik/boolean.hpp
@@ -28,10 +28,7 @@
 
 // std
 #include <iosfwd>
-#include <algorithm>
 #include <string>
-//#include <istream>
-//#include <ostream>
 
 namespace mapnik
 {
diff --git a/include/mapnik/util/conversions.hpp b/include/mapnik/util/conversions.hpp
index de5bd2f93..8a4c143c5 100644
--- a/include/mapnik/util/conversions.hpp
+++ b/include/mapnik/util/conversions.hpp
@@ -28,8 +28,7 @@
 #include <mapnik/value_types.hpp>
 
 // stl
-#include <string>
-#include <algorithm>
+#include <iosfwd>
 
 namespace mapnik { namespace util {
 
@@ -39,32 +38,8 @@ to avoid the compile time overhead given it is included
 by many other headers inside mapnik.
 */
 
-MAPNIK_DECL inline bool string2bool(std::string const& value, bool & result)
-{
-    if (value.empty() || value.size() > 5) {
-        return false;
-    } else if (value == "true") {
-        return result = true;
-    } else if (value == "false") {
-        result = false;
-        return true;
-    }
-    std::string val(value);
-    std::transform(val.begin(), val.end(), val.begin(), ::tolower);
-    if (val == "true" || val == "yes" || val == "1" || val == "on") {
-        return result = true;
-    } else if (val == "false" || val == "no" || val == "0" || val == "off") {
-        result = false;
-        return true;
-    }
-    return false;
-}
-
-MAPNIK_DECL inline bool string2bool(const char * iter, const char * end, bool & result)
-{
-    std::string val(iter,end);
-    return string2bool(val,result);
-}
+MAPNIK_DECL bool string2bool(std::string const& value, bool & result);
+MAPNIK_DECL bool string2bool(const char * iter, const char * end, bool & result);
 
 MAPNIK_DECL bool string2int(std::string const& value, int & result);
 MAPNIK_DECL bool string2int(const char * iter, const char * end, int & result);
diff --git a/src/conversions.cpp b/src/conversions.cpp
index 250378e0e..83bdd5fae 100644
--- a/src/conversions.cpp
+++ b/src/conversions.cpp
@@ -56,6 +56,33 @@ auto LONGLONG = qi::long_long_type();
 auto FLOAT = qi::float_type();
 auto DOUBLE = qi::double_type();
 
+bool string2bool(std::string const& value, bool & result)
+{
+    if (value.empty() || value.size() > 5) {
+        return false;
+    } else if (value == "true") {
+        return result = true;
+    } else if (value == "false") {
+        result = false;
+        return true;
+    }
+    std::string val(value);
+    std::transform(val.begin(), val.end(), val.begin(), ::tolower);
+    if (val == "true" || val == "yes" || val == "1" || val == "on") {
+        return result = true;
+    } else if (val == "false" || val == "no" || val == "0" || val == "off") {
+        result = false;
+        return true;
+    }
+    return false;
+}
+
+bool string2bool(const char * iter, const char * end, bool & result)
+{
+    std::string val(iter,end);
+    return string2bool(val,result);
+}
+
 bool string2int(const char * iter, const char * end, int & result)
 {
     ascii::space_type space;