diff --git a/constraint.cpp b/constraint.cpp
index 8fb0c5a..e6cdadc 100644
--- a/constraint.cpp
+++ b/constraint.cpp
@@ -103,6 +103,16 @@ void Constraint::ConstrainCoincident(hEntity ptA, hEntity ptB) {
 }
 
 void Constraint::MenuConstrain(int id) {
+    if(SK.constraint.n > 30) {
+        if((!SS.license.licensed) && SS.license.trialDaysRemaining <= 0) {
+            Error("The 90-day trial of SolveSpace has expired, and the light "
+                  "version does not support more than 30 constraints in a "
+                  "single file.\r\n\r\n"
+                  "Choose Help -> Website / Manual to purchase a license.");
+            return;
+        }
+    }
+
     Constraint c;
     ZERO(&c);
     c.group = SS.GW.activeGroup;
diff --git a/group.cpp b/group.cpp
index 7535d4b..f8705d6 100644
--- a/group.cpp
+++ b/group.cpp
@@ -17,14 +17,6 @@ void Group::AddParam(IdList<Param,hParam> *param, hParam hp, double v) {
 }
 
 void Group::MenuGroup(int id) {
-    if(!SS.license.licensed && SK.group.n >= 7) {
-        Error("The free version of this software does not support more "
-              "than six groups.\r\n\r\n"
-              "To remove this restriction, please choose Help -> "
-              "Website / Manual, and purchase a license.");
-        return;
-    }
-
     Group g;
     ZERO(&g);
     g.visible = true;
diff --git a/solvespace.cpp b/solvespace.cpp
index a1a1d82..43ff666 100644
--- a/solvespace.cpp
+++ b/solvespace.cpp
@@ -12,6 +12,23 @@ void SolveSpace::CheckLicenseFromRegistry(void) {
 
     license.licensed =
         LicenseValid(license.line1, license.line2, license.users, license.key);
+
+    // Now see if we've recorded a previous first use time in the registry. If
+    // yes then we use that, otherwise we record the current time.
+    SQWORD now = GetUnixTime();
+    DWORD timeLow  = CnfThawDWORD(0, "FirstUseLow");
+    DWORD timeHigh = CnfThawDWORD(0, "FirstUseHigh");
+    if(timeHigh == 0 && timeLow == 0) {
+        CnfFreezeDWORD((DWORD)((now      ) & 0xffffffff), "FirstUseLow");
+        CnfFreezeDWORD((DWORD)((now >> 32) & 0xffffffff), "FirstUseHigh");
+        license.firstUse = now;
+    } else {
+        license.firstUse = (((SQWORD)timeHigh) << 32) | ((SQWORD)timeLow);
+    }
+
+    const int SECONDS_IN_DAY = 60*60*24;
+    license.trialDaysRemaining = 90 -
+        (int)(((now - license.firstUse))/SECONDS_IN_DAY);
 }
 
 void SolveSpace::Init(char *cmdLine) {
@@ -257,6 +274,7 @@ void SolveSpace::AddToRecentList(char *file) {
 }
 
 bool SolveSpace::GetFilenameAndSave(bool saveAs) {
+
     char newFile[MAX_PATH];
     strcpy(newFile, saveFile);
     if(saveAs || strlen(newFile)==0) {
diff --git a/solvespace.h b/solvespace.h
index cc05b14..98c97d8 100644
--- a/solvespace.h
+++ b/solvespace.h
@@ -44,6 +44,7 @@ inline double WRAP_SYMMETRIC(double v, double n) {
 #define isforname(c) (isalnum(c) || (c) == '_' || (c) == '-' || (c) == '#')
 
 typedef unsigned __int64 QWORD;
+typedef signed __int64 SQWORD;
 typedef signed long SDWORD;
 typedef signed short SWORD;
 
@@ -118,6 +119,7 @@ void InvalidateGraphics(void);
 void PaintGraphics(void);
 void GetGraphicsWindowSize(int *w, int *h);
 SDWORD GetMilliseconds(void);
+SQWORD GetUnixTime(void);
 
 void dbp(char *str, ...);
 #define DBPTRI(tri) \
@@ -636,11 +638,13 @@ public:
     };
     Crc crc;
     struct {
-        bool licensed;
-        char line1[512];
-        char line2[512];
-        char users[512];
-        DWORD key;
+        bool    licensed;
+        char    line1[512];
+        char    line2[512];
+        char    users[512];
+        DWORD   key;
+        SQWORD  firstUse;
+        int     trialDaysRemaining;
     } license;
     static void MenuHelp(int id);
     void CleanEol(char *s);
diff --git a/textscreens.cpp b/textscreens.cpp
index 3a37f5d..a46bfe3 100644
--- a/textscreens.cpp
+++ b/textscreens.cpp
@@ -157,7 +157,13 @@ void TextWindow::ShowListOfGroups(void) {
         Printf(false, "%Fg  %s", SS.license.users);
     } else {
         Printf(false, "%Fx*** NO LICENSE FILE IS PRESENT ***");
-        Printf(false, "%Fx  eval / non-commercial use only");
+        if(SS.license.trialDaysRemaining > 0) {
+            Printf(false, "%Fx  running as full demo, %d day%s remaining",
+                SS.license.trialDaysRemaining,
+                SS.license.trialDaysRemaining == 1 ? "" : "s");
+        } else {
+            Printf(false, "%Fx  demo expired, now running in light mode");
+        }
         Printf(false, "%Fx  buy at %Fl%f%Llhttp://www.solvespace.com/%E",
             &ScreenGoToWebsite);
     }
diff --git a/win32/w32main.cpp b/win32/w32main.cpp
index ac99a75..6ad5c3e 100644
--- a/win32/w32main.cpp
+++ b/win32/w32main.cpp
@@ -7,6 +7,7 @@
 #include <stdarg.h>
 #include <string.h>
 #include <stdio.h>
+#include <time.h>
 
 #include "solvespace.h"
 
@@ -598,6 +599,13 @@ SDWORD GetMilliseconds(void)
     return (SDWORD)d;
 }
 
+SQWORD GetUnixTime(void)
+{
+    __time64_t ret;
+    _time64(&ret);
+    return ret;
+}
+
 void InvalidateText(void)
 {
     InvalidateRect(TextWnd, NULL, FALSE);