diff --git a/src/bsdfs/blendbsdf.cpp b/src/bsdfs/blendbsdf.cpp
index 3d7f6617..887cf38c 100644
--- a/src/bsdfs/blendbsdf.cpp
+++ b/src/bsdfs/blendbsdf.cpp
@@ -24,7 +24,7 @@
 MTS_NAMESPACE_BEGIN
 
 /*! \plugin{blendbsdf}{Blended material}
- * \order{16}
+ * \order{17}
  * \parameters{
  *     \parameter{weight}{\Float\Or\Texture}{A floating point value or texture
  *      with values between zero and one. The extreme values zero and one activate the
diff --git a/src/bsdfs/bumpmap.cpp b/src/bsdfs/bumpmap.cpp
index 8de46dc6..0dab142a 100644
--- a/src/bsdfs/bumpmap.cpp
+++ b/src/bsdfs/bumpmap.cpp
@@ -113,6 +113,11 @@ public:
 		} else if (child->getClass()->derivesFrom(MTS_CLASS(Texture))) {
 			if (m_displacement != NULL)
 				Log(EError, "Only a single displacement texture can be specified!");
+			const Properties &props = child->getProperties();
+			if (props.getPluginName() == "bitmap" && !props.hasProperty("gamma"))
+				Log(EError, "When using a bitmap texture as a bump map, please explicitly specify "
+						"the 'gamma' parameter of the bitmap plugin. In most cases the following is the correct choice: "
+						"<float name=\"gamma\" value=\"1.0\"/>");
 			m_displacement = static_cast<Texture *>(child);
 		} else {
 			BSDF::addChild(name, child);
diff --git a/src/bsdfs/mask.cpp b/src/bsdfs/mask.cpp
index 0a426f7b..d34e368a 100644
--- a/src/bsdfs/mask.cpp
+++ b/src/bsdfs/mask.cpp
@@ -22,7 +22,7 @@
 MTS_NAMESPACE_BEGIN
 
 /*!\plugin{mask}{Opacity mask}
- * \order{17}
+ * \order{18}
  * \parameters{
  *     \parameter{opacity}{\Spectrum\Or\Texture}{
  *          Specifies the per-channel opacity (where $1=$ completely opaque)\default{0.5}.
diff --git a/src/bsdfs/mixturebsdf.cpp b/src/bsdfs/mixturebsdf.cpp
index 533d5371..7baad5ab 100644
--- a/src/bsdfs/mixturebsdf.cpp
+++ b/src/bsdfs/mixturebsdf.cpp
@@ -23,7 +23,7 @@
 MTS_NAMESPACE_BEGIN
 
 /*! \plugin{mixturebsdf}{Mixture material}
- * \order{15}
+ * \order{16}
  * \parameters{
  *     \parameter{weights}{\String}{A comma-separated list of BSDF weights}
  *     \parameter{\Unnamed}{\BSDF}{Multiple BSDF instances that should be
diff --git a/src/bsdfs/normalmap.cpp b/src/bsdfs/normalmap.cpp
index 4b46f0ab..ec131050 100644
--- a/src/bsdfs/normalmap.cpp
+++ b/src/bsdfs/normalmap.cpp
@@ -21,6 +21,29 @@
 
 MTS_NAMESPACE_BEGIN
 
+/*! \plugin{normalmap}{Normal map modifier}
+ * \order{13}
+ * \icon{bsdf_bumpmap}
+ *
+ * \parameters{
+ *     \parameter{\Unnamed}{\Texture}{
+ *       The color values of this texture specify the perturbed
+ *       normals relative in the local surface coordinate system.
+ *     }
+ *     \parameter{\Unnamed}{\BSDF}{A BSDF model that should
+ *     be affected by the normal map}
+ * }
+ *
+ * This plugin is conceptually similar to the \pluginref{bump} map plugin
+ * but uses a normal map instead of a bump map. A normal map is a RGB texture, whose color channels
+ * encode the XYZ coordinates of the desired surface normals.
+ * These are specified \emph{relative} to the local shading frame,
+ * which means that a normal map with a value of $(0,0,1)$ everywhere
+ * causes no changes to the surface.
+ * To turn the 3D normal directions into (nonnegative) color values
+ * suitable for this plugin, the
+ * mapping $x \mapsto (x+1)/2$ must be applied to each component.
+ */
 class NormalMap : public BSDF {
 public:
 	NormalMap(const Properties &props) : BSDF(props) { }
@@ -61,7 +84,12 @@ public:
 			m_nested = static_cast<BSDF *>(child);
 		} else if (child->getClass()->derivesFrom(MTS_CLASS(Texture))) {
 			if (m_normals != NULL)
-				Log(EError, "Only a single normals texture can be specified!");
+				Log(EError, "Only a single normal texture can be specified!");
+			const Properties &props = child->getProperties();
+			if (props.getPluginName() == "bitmap" && !props.hasProperty("gamma"))
+				Log(EError, "When using a bitmap texture as a normal map, please explicitly specify "
+						"the 'gamma' parameter of the bitmap plugin. In most cases the following is the correct choice: "
+						"<float name=\"gamma\" value=\"1.0\"/>");
 			m_normals = static_cast<Texture *>(child);
 		} else {
 			BSDF::addChild(name, child);
@@ -192,7 +220,7 @@ protected:
 // ================ Hardware shader implementation ================
 
 /**
- * This is a quite approximate version of the bump map model -- it likely
+ * This is a quite approximate version of the normal map model -- it likely
  * won't match the reference exactly, but it should be good enough for
  * preview purposes
  */
diff --git a/src/bsdfs/phong.cpp b/src/bsdfs/phong.cpp
index 8130d600..6b029940 100644
--- a/src/bsdfs/phong.cpp
+++ b/src/bsdfs/phong.cpp
@@ -23,7 +23,7 @@
 MTS_NAMESPACE_BEGIN
 
 /*!\plugin{phong}{Modified Phong BRDF}
- * \order{13}
+ * \order{14}
  * \parameters{
  *     \parameter{exponent}{\Float\Or\Texture}{
  *         Specifies the Phong exponent \default{30}.
diff --git a/src/bsdfs/twosided.cpp b/src/bsdfs/twosided.cpp
index 8593741e..6fa51d04 100644
--- a/src/bsdfs/twosided.cpp
+++ b/src/bsdfs/twosided.cpp
@@ -23,7 +23,7 @@
 MTS_NAMESPACE_BEGIN
 
 /*!\plugin{twosided}{Two-sided BRDF adapter}
- * \order{18}
+ * \order{19}
  * \parameters{
  *     \parameter{\Unnamed}{\BSDF}{A nested BRDF that should
  *     be turned into a two-sided scattering model. If two BRDFs
diff --git a/src/bsdfs/ward.cpp b/src/bsdfs/ward.cpp
index 596419ff..9e2cde9c 100644
--- a/src/bsdfs/ward.cpp
+++ b/src/bsdfs/ward.cpp
@@ -24,7 +24,7 @@
 MTS_NAMESPACE_BEGIN
 
 /*!\plugin{ward}{Anisotropic Ward BRDF}
- * \order{14}
+ * \order{15}
  * \parameters{
  *     \parameter{variant}{\String}{
  *         Determines the variant of the Ward model to use: