diff --git a/CHANGELOG.md b/CHANGELOG.md
index cc890d1f..93f09eb6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,7 @@
 * Fix various incorrect usages of the FGD `frustum()` helper.
 * Normals are now correctly calculated when generating propcombined models. This requires all previous models to be rebuilt, unfortunately.
 * Fix overlays not functioning with `material_modify_control` parent searching.
+* #274: Force `light_environment` to use the required `SunSpreadAngle` casing.
 
 
 --------------------
diff --git a/fgd/point/light/light_directional.fgd b/fgd/point/light/light_directional.fgd
index 19c72344..f73a0e12 100644
--- a/fgd/point/light/light_directional.fgd
+++ b/fgd/point/light/light_directional.fgd
@@ -8,7 +8,8 @@
 	_light(color255) : "Brightness" : "255 255 255 200"
 	_lighthdr(color255) : "BrightnessHDR" : "-1 -1 -1 1"
 	_lightscalehdr(float) : "BrightnessScaleHDR" : 0.7 : "Amount to scale the light by when compiling for HDR."
-	sunspreadangle(float) : "SpreadAngle" : 0 : "The angular extent of the light for casting soft shadows. Higher numbers are more diffuse. 5 is a good starting value."
+	// VRAD requires this casing for the key name.
+	SunSpreadAngle(float) : "SpreadAngle" : 0 : "The angular extent of the light for casting soft shadows. Higher numbers are more diffuse. 5 is a good starting value."
 
 	@resources []
 	]
diff --git a/fgd/point/light/light_environment.fgd b/fgd/point/light/light_environment.fgd
index 3a62654d..d3f09f7a 100644
--- a/fgd/point/light/light_environment.fgd
+++ b/fgd/point/light/light_environment.fgd
@@ -13,7 +13,8 @@
 	_lightscalehdr(float) : "BrightnessScaleHDR" : 1 : "Amount to scale the light by when compiling for HDR."
 	_ambienthdr(color255) : "AmbientHDR" : "-1 -1 -1 1"
 	_ambientscalehdr(float) : "AmbientScaleHDR" : 1 : "Amount to scale the ambient light by when compiling for hdr."
-	sunspreadangle(float) : "SunSpreadAngle" : 5 : "The angular extent of the sun for casting soft shadows. Higher numbers are more diffuse. 5 is a good starting value."
+	// VRAD requires this casing for the key name.
+	SunSpreadAngle(float) : "SunSpreadAngle" : 5 : "The angular extent of the sun for casting soft shadows. Higher numbers are more diffuse. 5 is a good starting value."
 
 	@resources []
 	]
diff --git a/transforms/fgd_tweaks/light_sun_spread_angle.py b/transforms/fgd_tweaks/light_sun_spread_angle.py
new file mode 100644
index 00000000..d307a092
--- /dev/null
+++ b/transforms/fgd_tweaks/light_sun_spread_angle.py
@@ -0,0 +1,10 @@
+"""This keyvalue is case-sensitive, force the required casing."""
+from hammeraddons.bsp_transform import Context, trans
+
+
+@trans('FGD - Fix Sun Spread Angle')
+def light_sun_spread_angle(ctx: Context) -> None:
+    """Force case-sensitivity on this keyvalue."""
+    for ent in ctx.vmf.by_class['light_environment'] | ctx.vmf.by_class['light_directional']:
+        ent['SunSpreadAngle'] = ent.pop('sunspreadangle')
+        print(dict(ent.items()))