diff --git a/src/m_perfstats.c b/src/m_perfstats.c
index 4f3b11a0e..e3cb03ce4 100644
--- a/src/m_perfstats.c
+++ b/src/m_perfstats.c
@@ -453,7 +453,7 @@ static void M_DrawTickStats(void)
 						regularcount++;
 				}
 			}
-			else if (i == THINK_DYNSLOPE)
+			else if (i == THINK_DYNSLOPE || i == THINK_DYNSLOPEDEMO)
 				dynslopethcount++;
 			else if (i == THINK_PRECIP)
 				precipcount++;
diff --git a/src/p_local.h b/src/p_local.h
index 19e311911..6339204ae 100644
--- a/src/p_local.h
+++ b/src/p_local.h
@@ -64,10 +64,12 @@ extern "C" {
 
 typedef enum
 {
+	THINK_DYNSLOPE,
 	THINK_POLYOBJ,
 	THINK_MAIN,
 	THINK_MOBJ,
-	THINK_DYNSLOPE,
+	// This is kept for backwards compat with old demos.
+	THINK_DYNSLOPEDEMO, 
 
 	// Lists after this may exist but they do not call an
 	// action in P_RunThinkers
diff --git a/src/p_slopes.c b/src/p_slopes.c
index d18f62fb9..c9bf22117 100644
--- a/src/p_slopes.c
+++ b/src/p_slopes.c
@@ -305,7 +305,8 @@ static inline void P_AddDynLineSlopeThinker (pslope_t* slope, dynplanetype_t typ
 	th->type = type;
 	th->sourceline = sourceline;
 	th->extent = extent;
-	P_AddThinker(THINK_DYNSLOPE, &th->thinker);
+	// Handle old demos as well.
+	P_AddThinker(/*G_CompatLevel(0x000D) ? THINK_DYNSLOPEDEMO :*/ THINK_DYNSLOPE, &th->thinker);
 
 	// interpolation
 	R_CreateInterpolator_DynSlope(&th->thinker, slope);
@@ -333,7 +334,8 @@ static inline void P_AddDynVertexSlopeThinker (pslope_t* slope, const INT16 tags
 		if (lines[l].args[0])
 			th->relative |= 1<<i;
 	}
-	P_AddThinker(THINK_DYNSLOPE, &th->thinker);
+	// Handle old demos as well.
+	P_AddThinker(/*G_CompatLevel(0x000D) ? THINK_DYNSLOPEDEMO :*/ THINK_DYNSLOPE, &th->thinker);
 }
 
 /// Create a new slope and add it to the slope list.