diff --git a/source/gui/Scripting/JSInterface_CGUISize.cpp b/source/gui/Scripting/JSInterface_CGUISize.cpp
index 7f447e6957..fa1df5ac94 100644
--- a/source/gui/Scripting/JSInterface_CGUISize.cpp
+++ b/source/gui/Scripting/JSInterface_CGUISize.cpp
@@ -81,10 +81,10 @@ bool SetCRectField(JSContext* cx, unsigned argc, JS::Value* vp)
 }
 
 // Produces "10", "-10", "50%", "50%-10", "50%+10", etc
-CStr ToPercentString(double pix, double per)
+std::string ToPercentString(double pix, double per)
 {
 	if (per == 0)
-		return CStr::FromDouble(pix);
+		return fmt::format("{}", pix);
 
 	if (pix == 0)
 		return fmt::format("{}%", per);
@@ -97,7 +97,7 @@ bool toString(JSContext* cx, uint argc, JS::Value* vp)
 	JS::CallArgs args{JS::CallArgsFromVp(argc, vp)};
 	JS::RootedObject obj{cx, &args.thisv().toObject()};
 	CGUISimpleSetting<CGUISize>* wrapper{JS::GetMaybePtrFromReservedSlot<CGUISimpleSetting<CGUISize>>(obj, Script::Interface::JSObjectReservedSlots::PRIVATE)};
-	CStr buffer;
+	std::string buffer;
 
 	buffer += ToPercentString(wrapper->GetMutable().pixel.left, wrapper->GetMutable().percent.left) + " ";
 	buffer += ToPercentString(wrapper->GetMutable().pixel.top, wrapper->GetMutable().percent.top) + " ";
diff --git a/source/gui/Scripting/JSInterface_GUISize.cpp b/source/gui/Scripting/JSInterface_GUISize.cpp
index 1f9c7e0918..9656328fef 100644
--- a/source/gui/Scripting/JSInterface_GUISize.cpp
+++ b/source/gui/Scripting/JSInterface_GUISize.cpp
@@ -106,18 +106,21 @@ bool JSI_GUISize::construct(JSContext* cx, uint argc, JS::Value* vp)
 }
 
 // Produces "10", "-10", "50%", "50%-10", "50%+10", etc
-CStr JSI_GUISize::ToPercentString(double pix, double per)
+std::string JSI_GUISize::ToPercentString(double pix, double per)
 {
 	if (per == 0)
-		return CStr::FromDouble(pix);
+		return fmt::format("{}", pix);
 
-	return CStr::FromDouble(per)+"%"+(pix == 0.0 ? CStr() : pix > 0.0 ? CStr("+")+CStr::FromDouble(pix) : CStr::FromDouble(pix));
+	if (pix == 0.0)
+		return fmt::format("{}%", per);
+
+	return fmt::format("{}%{:+}", per, pix);
 }
 
 bool JSI_GUISize::toString(JSContext* cx, uint argc, JS::Value* vp)
 {
 	JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
-	CStr buffer;
+	std::string buffer;
 
 	Script::Request rq(cx);
 	double val, valr;
diff --git a/source/gui/Scripting/JSInterface_GUISize.h b/source/gui/Scripting/JSInterface_GUISize.h
index c2250d5e04..a3dc798a23 100644
--- a/source/gui/Scripting/JSInterface_GUISize.h
+++ b/source/gui/Scripting/JSInterface_GUISize.h
@@ -21,7 +21,8 @@
 
 #include "lib/posix/posix_types.h"
 #include "lib/types.h"
-#include "ps/CStr.h"
+
+#include <string>
 
 namespace JS { class Value; }
 namespace Script { class Interface; }
@@ -43,7 +44,7 @@ namespace JSI_GUISize
 	bool construct(JSContext* cx, uint argc, JS::Value* vp);
 	bool toString(JSContext* cx, uint argc, JS::Value* vp);
 
-	CStr ToPercentString(double pix, double per);
+	std::string ToPercentString(double pix, double per);
 }
 
 #endif // INCLUDED_JSI_GUISIZE
diff --git a/source/network/scripting/JSInterface_Network.cpp b/source/network/scripting/JSInterface_Network.cpp
index 83cd27d970..279dd4a1ef 100644
--- a/source/network/scripting/JSInterface_Network.cpp
+++ b/source/network/scripting/JSInterface_Network.cpp
@@ -280,9 +280,9 @@ void SendNetworkFlare(JS::HandleValue position)
 	// (TODO?): Converting the doubles into strings here is a workaround because direct (de)serialisation of floating point numbers is not supported.
 	// It causes somewhat awkward message handling, but the resulting efficiency losses are negligible.
 	g_NetClient->SendFlareMessage(
-		CStr::FromDouble(positionX.toNumber()),
-		CStr::FromDouble(positionY.toNumber()),
-		CStr::FromDouble(positionZ.toNumber())
+		fmt::format("{}", positionX.toNumber()),
+		fmt::format("{}", positionY.toNumber()),
+		fmt::format("{}", positionZ.toNumber())
 	);
 }
 
diff --git a/source/ps/CStr.cpp b/source/ps/CStr.cpp
index cedab6cde7..6693a272cb 100644
--- a/source/ps/CStr.cpp
+++ b/source/ps/CStr.cpp
@@ -200,15 +200,6 @@ CStr CStr::Repeat(const CStr& str, size_t reps)
 	return ret;
 }
 
-// Construction from numbers:
-
-CStr CStr::FromDouble(double n)
-{
-	tstringstream<StrBase> ss;
-	ss << n;
-	return ss.str();
-}
-
 // Conversion to numbers:
 
 int CStr::ToInt() const
diff --git a/source/ps/CStr.h b/source/ps/CStr.h
index cf7e36cae4..85ff427842 100644
--- a/source/ps/CStr.h
+++ b/source/ps/CStr.h
@@ -95,8 +95,6 @@ public:
 
 	// Conversions:
 
-	static CStr FromDouble(double n);
-
 	/**
 	 * Return CStr as Integer.
 	 * Conversion is from the beginning of CStr.
diff --git a/source/ps/UserReport.cpp b/source/ps/UserReport.cpp
index 59d86cf892..eb7ad21bfa 100644
--- a/source/ps/UserReport.cpp
+++ b/source/ps/UserReport.cpp
@@ -449,7 +449,8 @@ private:
 			self->m_RequestDataOffset += amount;
 		}
 
-		self->SetStatus("sending:" + CStr::FromDouble((double)self->m_RequestDataOffset / self->m_RequestData.size()));
+		self->SetStatus(fmt::format("sending:{:L}",
+			static_cast<double>(self->m_RequestDataOffset) / self->m_RequestData.size()));
 
 		return amount;
 	}