diff --git a/Dockerfile.centos7 b/Dockerfile.centos7
index ad1e620b..d8d8deeb 100644
--- a/Dockerfile.centos7
+++ b/Dockerfile.centos7
@@ -11,7 +11,7 @@ RUN sed -i s/mirror.centos.org/vault.centos.org/g /etc/yum.repos.d/*.repo \
 RUN sed -i s/mirror.centos.org/vault.centos.org/g /etc/yum.repos.d/*.repo \
     && sed -i s/^#.*baseurl=http/baseurl=http/g /etc/yum.repos.d/*.repo \
     && sed -i s/^mirrorlist=http/#mirrorlist=http/g /etc/yum.repos.d/*.repo \ 
-    && yum install -y devtoolset-8 wget cmake3 make eigen3-devel tcl-devel tcl-tclreadline-devel swig3 bison flex zlib-devel \
+    && yum install -y devtoolset-8 wget cmake3 make eigen3-devel tcl-devel tcl-tclreadline-devel swig3 bison flex zlib-devel valgrind \
     && yum clean -y all
 
 # Download CUDD
diff --git a/Dockerfile.ubuntu22.04 b/Dockerfile.ubuntu22.04
index bee8b31e..4bc5ea9d 100644
--- a/Dockerfile.ubuntu22.04
+++ b/Dockerfile.ubuntu22.04
@@ -16,7 +16,8 @@ RUN apt-get update && \
     bison \
     flex \
     automake \
-    autotools-dev
+    autotools-dev \
+    valgrind
 
 # Download CUDD
 RUN wget https://raw.githubusercontent.com/davidkebo/cudd/main/cudd_versions/cudd-3.0.0.tar.gz && \
diff --git a/sdc/Sdc.tcl b/sdc/Sdc.tcl
index 75b4b813..b2382800 100644
--- a/sdc/Sdc.tcl
+++ b/sdc/Sdc.tcl
@@ -72,10 +72,10 @@ proc source_ { filename echo verbose } {
   if [catch {open $filename r} stream] {
     sta_error 340 "cannot open '$filename'."
   } else {
-    if { [info commands zlib] == "" } {
-      sta_error 339 "tcl version > 8.6 required for zlib support."
-    }
     if { [file extension $filename] == ".gz" } {
+      if { [info commands zlib] == "" } {
+        sta_error 339 "tcl version > 8.6 required for zlib support."
+      }
       zlib push gunzip $stream
     }
     # Save file and line in recursive call to source.
diff --git a/test/regression.tcl b/test/regression.tcl
index 260c6cec..1beb7090 100755
--- a/test/regression.tcl
+++ b/test/regression.tcl
@@ -75,6 +75,9 @@ proc parse_args {} {
       lappend app_options $threads
       set argv [lrange $argv 2 end]
     } elseif { $arg == "-valgrind" } {
+      if { ![find_valgrind] } {
+        error "valgrind not found."
+      }
       set use_valgrind 1
       set argv [lrange $argv 1 end]
     } elseif { $arg == "-report_stats" } {
@@ -92,6 +95,18 @@ proc parse_args {} {
   }
 }
 
+# Find valgrind in $PATH.
+proc find_valgrind {} {
+  global env
+
+  foreach dir [regsub -all ":" $env(PATH) " "] {
+    if { [file executable [file join $dir "valgrind"]] } {
+      return 1
+    }
+  }
+  return 0
+}
+
 proc expand_tests { argv } {
   global test_groups errors