diff --git a/app/win/download-nsis-plugins b/app/win/download-nsis-plugins
index f02c60e77b..6e067b267d 100755
--- a/app/win/download-nsis-plugins
+++ b/app/win/download-nsis-plugins
@@ -46,6 +46,11 @@ for plugin in $plugins; do
 	curl https://hg.mozilla.org/mozilla-central/raw-file/052d53200cf8/other-licenses/nsis/Plugins/$plugin.dll > $plugin.dll
 done
 
+curl https://nsis.sourceforge.io/mediawiki/images/1/18/NsProcess.zip > NsProcess.zip
+7z e NsProcess.zip "Plugin/nsProcessW.dll"
+mv nsProcessW.dll nsProcess.dll
+rm NsProcess.zip
+
 echo
 echo
 echo "Files downloaded to ./Plugins -- move to ${NSIS_DIR}Plugins"
diff --git a/app/win/installer/installer.nsi b/app/win/installer/installer.nsi
index 2aa6115d36..5e1154c39c 100755
--- a/app/win/installer/installer.nsi
+++ b/app/win/installer/installer.nsi
@@ -59,6 +59,7 @@ Var InstallType
 !insertmacro WordFind
 !insertmacro WordReplace
 
+!include nsProcess.nsh
 ; The following includes are custom.
 !include branding.nsi
 !include defines.nsi
@@ -962,6 +963,21 @@ Function .onInit
     ${EndIf}
   !endif
 
+  # Check if Zotero is running. If it is, prompt the user to close Zotero and exit.
+  # For silent installs, kill Zotero and if successful, continue with the install.
+  ${nsProcess::FindProcess} ${FileMainEXE} $R0
+  ${If} $R0 = 0
+    IfSilent +3
+    MessageBox MB_OK|MB_ICONSTOP "Zotero is already running. Please close Zotero before running the installer."
+    Quit
+    ${nsProcess::KillProcess} ${FileMainEXE} $R0
+    Sleep 500
+    ${nsProcess::FindProcess} ${FileMainEXE} $R0
+    ${If} $R0 = 0
+      Quit
+    ${EndIf}
+  ${EndIf}
+
   StrCpy $R1 "Zotero Standalone"
   StrCpy $R2 "An older version of Zotero is installed. If you continue, the existing version will be removed.$\n$\nYour Zotero data will not be affected."
   Call UninstallOld
diff --git a/app/win/installer/nsProcess.nsh b/app/win/installer/nsProcess.nsh
new file mode 100644
index 0000000000..279f581147
--- /dev/null
+++ b/app/win/installer/nsProcess.nsh
@@ -0,0 +1,28 @@
+!define nsProcess::FindProcess `!insertmacro nsProcess::FindProcess`
+
+!macro nsProcess::FindProcess _FILE _ERR
+	nsProcess::_FindProcess /NOUNLOAD `${_FILE}`
+	Pop ${_ERR}
+!macroend
+
+
+!define nsProcess::KillProcess `!insertmacro nsProcess::KillProcess`
+
+!macro nsProcess::KillProcess _FILE _ERR
+	nsProcess::_KillProcess /NOUNLOAD `${_FILE}`
+	Pop ${_ERR}
+!macroend
+
+!define nsProcess::CloseProcess `!insertmacro nsProcess::CloseProcess`
+
+!macro nsProcess::CloseProcess _FILE _ERR
+	nsProcess::_CloseProcess /NOUNLOAD `${_FILE}`
+	Pop ${_ERR}
+!macroend
+
+
+!define nsProcess::Unload `!insertmacro nsProcess::Unload`
+
+!macro nsProcess::Unload
+	nsProcess::_Unload
+!macroend