diff --git a/src/libstore/nar-info.cc b/src/libstore/nar-info.cc
index 274cd861c..d17253741 100644
--- a/src/libstore/nar-info.cc
+++ b/src/libstore/nar-info.cc
@@ -7,15 +7,18 @@ namespace nix {
 NarInfo::NarInfo(const Store & store, const std::string & s, const std::string & whence)
     : ValidPathInfo(StorePath(StorePath::dummy), Hash(Hash::dummy)) // FIXME: hack
 {
-    auto corrupt = [&]() {
-        return Error("NAR info file '%1%' is corrupt", whence);
+    unsigned line = 1;
+
+    auto corrupt = [&](const char * reason) {
+        return Error("NAR info file '%1%' is corrupt: %2%", whence,
+            std::string(reason) + (line > 0 ? " at line " + std::to_string(line) : ""));
     };
 
     auto parseHashField = [&](const std::string & s) {
         try {
             return Hash::parseAnyPrefixed(s);
         } catch (BadHash &) {
-            throw corrupt();
+            throw corrupt("bad hash");
         }
     };
 
@@ -26,12 +29,12 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
     while (pos < s.size()) {
 
         size_t colon = s.find(':', pos);
-        if (colon == std::string::npos) throw corrupt();
+        if (colon == std::string::npos) throw corrupt("expecting ':'");
 
         std::string name(s, pos, colon - pos);
 
         size_t eol = s.find('\n', colon + 2);
-        if (eol == std::string::npos) throw corrupt();
+        if (eol == std::string::npos) throw corrupt("expecting '\\n'");
 
         std::string value(s, colon + 2, eol - colon - 2);
 
@@ -47,7 +50,7 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
             fileHash = parseHashField(value);
         else if (name == "FileSize") {
             auto n = string2Int<decltype(fileSize)>(value);
-            if (!n) throw corrupt();
+            if (!n) throw corrupt("invalid FileSize");
             fileSize = *n;
         }
         else if (name == "NarHash") {
@@ -56,12 +59,12 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
         }
         else if (name == "NarSize") {
             auto n = string2Int<decltype(narSize)>(value);
-            if (!n) throw corrupt();
+            if (!n) throw corrupt("invalid NarSize");
             narSize = *n;
         }
         else if (name == "References") {
             auto refs = tokenizeString<Strings>(value, " ");
-            if (!references.empty()) throw corrupt();
+            if (!references.empty()) throw corrupt("extra References");
             for (auto & r : refs)
                 references.insert(StorePath(r));
         }
@@ -72,17 +75,26 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
         else if (name == "Sig")
             sigs.insert(value);
         else if (name == "CA") {
-            if (ca) throw corrupt();
+            if (ca) throw corrupt("extra CA");
             // FIXME: allow blank ca or require skipping field?
             ca = ContentAddress::parseOpt(value);
         }
 
         pos = eol + 1;
+        line += 1;
     }
 
     if (compression == "") compression = "bzip2";
 
-    if (!havePath || !haveNarHash || url.empty() || narSize == 0) throw corrupt();
+    if (!havePath || !haveNarHash || url.empty() || narSize == 0) {
+        line = 0; // don't include line information in the error
+        throw corrupt(
+            !havePath ? "StorePath missing" :
+            !haveNarHash ? "NarHash missing" :
+            url.empty() ? "URL missing" :
+            narSize == 0 ? "NarSize missing or zero"
+            : "?");
+    }
 }
 
 std::string NarInfo::to_string(const Store & store) const